Much research effort over the past years has gone into reconstructing the temperature history of the last millennium and beyond. The new IPCC report compiles a dozen reconstructions for the temperature of the Northern Hemisphere (including of course the original "hockey stick" reconstruction, despite opposite claims by the Wall Street Journal). Lack of data does not permit robust reconstructions for the Southern Hemisphere. Without exception, the reconstructions show that Northern Hemisphere temperatures are now higher than at any time during the past 1,000 years (Figure 1), confirming and strengthening the conclusions drawn in the previous IPCC report of 2001.

Fig. 1: Figure 6.10 (panel b) from the paleoclimate chapter of the current IPCC report (see there for details).

“Climate sceptics” do not like this and keep coming up with their own temperature histories. One of the weirdest has been circulated for years by German high-school teacher E.G. Beck (notorious for his equally weird CO2 curve). This history shows a medieval warm phase that is warmer than current climate by more than 1 ºC (see Figure 2). So how did Beck get this curve?

Fig. 2, modified from E.G. Beck (we added the green parts).

The curve is a fake in several respects. It originally is taken from the first IPCC report of 1990: a scan of the original is shown in Figure 3. At that time, no large-scale temperature reconstructions were available yet. To give an indication of past climate variability, the report showed Lamb’s Central England estimate. (Unfortunately this was not stated in the report – an oversight which shows that IPCC review procedures in the early days were not what they are now. We will post in more detail on the history of this curve another time.)

Fig. 3. The past millennium as shown in the first IPCC report of 1990, before quantitative large-scale reconstructions were available. This curve was based on Lamb's estimated climate history for central England.

But Beck did not stop at simply using this outdated curve, he modified it as highlighted in green in Figure 2. First, he added a wrong temperature scale – the tick marks in the old IPCC report represent 1 ºC, so Beck’s claimed range of 5 ºC exaggerates the past temperature variations by more than a factor of three. Second, the original curve only goes up to the 1970’s. Since then, Northern Hemisphere temperatures have increased by about 0.6 ºC and those in central England even more – so whatever you take this curve for, if it were continued to present, the current temperature would be above the Medieval level, as in the proper reconstructions available today. As this would destroy his message, Beck applied another fakery: he extended the curve flat up to the year 2000, thereby denying the measured warming since the 1970s. With this trick, his curve looks as if it was warmer in Medieval times then now.

When approached directly about these issues, Beck published a modified curve on a website. He changed the temperature range from 5 ºC to 4.5 ºC – but he shortened the arrow as well, so this was just cosmetics. He also added instrumental temperatures for the 20th Century at the end – but with his wrong temperature scale, they are completely out of proportion. (In fact his version suggests temperatures have warmed by 2 ºC since 1900, more than twice of what is actually observed!)

Beck goes even further: in a recent article (in German), he has the audacity to claim that his manipulated curve is right and the more recent scientific results shown by IPCC are wrong. And for years, he has offered his curve on an internet site (biokurs.de) that distributes teaching materials for schools, with support from German school authorities. It is quite likely that his fake curve has been shown (and will continue to be shown) to many school children.

On the same day the White Paper was published, [BP] announced that it
was scraping a £31bn plan to build a coal plant that would capture all
its carbon emissions and pump them under the sea bed. The company said
a delay in deciding whether the ambitious project deserved state
subsidy until 2008 meant that it was not worth pursuing

http://news.independent.co.uk/business/comment/article2586551.ece

Alternative fuel for thought

Gasoline has got to go, say big thinkers at the Future in Review
conference. But what the replacement will be is far from clear.

http://news.com.com/Alternative+fuel+for+thought/2100-11392_3-6186549.html?tag=nefd.lede

We've often been asked to provide a one stop link for resources that people can use to get up to speed on the issue of climate change, and so here is a first cut. Unlike our other postings, we'll amend this as we discover or are pointed to new resources. Different people have different needs and so we will group resources according to the level people start at.

For complete beginners:

NCAR: Weather and climate basics
Oxford University: The basics of climate prediction
Pew Center: Global Warming basics
Wikipedia: Global Warming
NASA: Global Warming update

Those with some knowledge:

The IPCC AR4 Frequently Asked Questions (pdf) is an excellent start. That covers:

• What Factors Determine Earth's Climate?
• What is the Relationship between Climate Change and Weather?
• What is the Greenhouse Effect?
• How do Human Activities Contribute to Climate Change and How do They Compare with Natural Influences?
• How are Temperatures on Earth Changing?
• How is Precipitation Changing?
• Has there been a Change in Extreme Events like Heat Waves, Droughts, Floods and Hurricanes?
• Is the Amount of Snow and Ice on the Earth Decreasing?
• Is Sea Level Rising?
• What Caused the Ice Ages and Other Important Climate Changes Before the Industrial Era?
• Is the Current Climate Change Unusual Compared to Earlier Changes in Earth's History?
• Are the Increases in Atmospheric Carbon Dioxide and Other Greenhouse Gases During the Industrial Era Caused by Human Activities?
• How Reliable Are the Models Used to Make Projections of Future Climate Change?
• Can Individual Extreme Events be Explained by Greenhouse Warming?
• Can the Warming of the 20th Century be Explained by Natural Variability?
• Are Extreme Events, Like Heat Waves, Droughts or Floods, Expected to Change as the Earth's Climate Changes?
• How Likely are Major or Abrupt Climate Changes, such as Loss of Ice Sheets or Changes in Global Ocean Circulation?
• If Emissions of Greenhouse Gases are Reduced, How Quickly do Their Concentrations in the Atmosphere Decrease?
• Do Projected Changes in Climate Vary from Region to Region?

We'll link to the individual pages once the report is available in html.

RealClimate: Start with our index

Informed, but in need of more detail:

Science: You can't do better than the IPCC reports themselves (AR4 2007, TAR 2001).

History: Spencer Weart's "Discovery of Global Warming" (AIP)

Art: Robert Rohde's "Global Warming Art'

Informed, but seeking serious discussion of common contrarian talking points:

All of the below links have indexed debunks of most of the common points of confusion:

• Coby Beck's How to talk to Global Warming Skeptic
• New Scientist: Climate Change: A guide for the perplexed
• RealClimate: Response to common contrarian arguments
• NERC (UK): Climate change debate summary
• UK Met Office: Climate Change Myths

Please feel free to suggest other suitable resources, particularly in different languages, and we'll try to keep this list up to date.

In my document “Biofuels Are Not the Answer”, I noted very briefly that biofuels will not “displace” fossil fuels. The attached note elaborates on this point.

Full Article (PDF)

 by Jeffrey Sachs

(more…)

(more…)

Lecture 1:
Bursting at the Seams

The 21st century will be marked by severe natural resource limits, the
rise of new economic powers and the threats of failed states. These are
tectonic changes with the potential to unleash global-scale upheavals.
Global cooperation of an unprecedented depth and scale will be needed
but we are not yet prepared for such cooperation.

Lecture 2:
Survival in the Anthropocene
The biggest challenges that we face - climate change, alleviation of
hunger, water stress, energy - are translated in the shadow of ignorance
into “us versus them” problems, with only the weakest links to
underlying scientific principles and technological options.

Lecture 3:
The Great Convergence

Power and America have seemed synonymous for the last fifty years. No
longer. Power in the 21st Century is shifting to the East: to India and
above all to China. Facing up to the end of centuries of North Atlantic
dominance - first Europe then the U.S. - will pose huge challenges.

Lecture 4:
Poverty in the Midst of Plenty

This lecture considers the challenges of extreme poverty and the extreme
worry of the rest of the world which fears for its own prosperity. It
spells out the limits of the free market to solve these problems and
proposes a plan of action which presents choices to those listening.

Lecture 5:
A New Politics for a New Age

The key political novelty of our age is mass political awareness and
mobilization. Mass mobilization has brought the Age of Empire to an end,
and accounts for the failures in Iraq. No society any longer tolerates
being ruled by another. Social mobilization can be a dramatic force for
positive change.

Climate change: ‘One [more] degree and we’re done for’

>
> New Scientist: 27 September 2006
>
> “Further global warming of 1 �C defines a critical threshold. Beyond
> that we will likely see changes that make Earth a different planet
> than the one we know.”
>
> So says Jim Hansen, director of NASA’s Goddard Institute for Space
> Studies in New York. Hansen and colleagues have analysed global
> temperature records and found that surface temperatures have been
> increasing by an average of 0.2 �C every decade for the past 30 years.
> Warming is greatest in the high latitudes of the northern hemisphere,
> particularly in the sub-Arctic boreal forests of Siberia and North
> America. Here the melting of ice and snow is exposing darker surfaces
> that absorb more sunlight and increase warming, creating a positive
> feedback.
>
> Earth is already as warm as at any time in the last 10,000 years, and
> is within 1 �C of being its hottest for a million years, says Hansen’s
> team. Another decade of business-as-usual carbon emissions will
> probably make it too late to prevent the ecosystems of the north from
> triggering runaway climate change, the study concludes (/Proceedings
> of the National Academy of Sciences/, vol 103, p 14288).
>
> The analysis reinforces a series of recent findings on accelerating
> environmental disruption in Siberia, northern Canada and Alaska,
> underlining a growing scientific consensus that these regions are
> pivotal to climate change. Earlier this month, NASA scientists
> reported that climate change was speeding up the melting of Arctic sea
> ice. Permanent sea ice has contracted by 14 per cent in the past two
> years (/Geophysical Research Letters/, vol 33, L17501). However,
> warming and melting have been just as dramatic on land in the far north.
>
> A meeting on Siberian climate change held in Leicester, UK, last week
> confirmed that Siberia has become a hotspot of global climate change.
> Geographer Heiko Balzter, of the University of Leicester, said central
> Siberia has warmed by almost 2 �C since 1970 - that’s three times the
> global average.
>
> Meanwhile, Stuart Chapin of the University of Alaska Fairbanks this
> week reported that air temperatures in the Alaskan interior have risen
> by 2 �C since 1950, and permafrost temperatures have risen by 2.5 �C
> (/Proceedings of the National Academy of Sciences/, DOI:
> 10.1073/pnas.0606955103).
>
> In Siberia the warming is especially pronounced in winter. “It has
> caused the onset of spring to advance by as much as one day a year
> since satellite observations began in 1982,” says Balzter. Similarly,
> Alaskan springs now arrive two weeks earlier than in 1950, according
> to Chapin.
>
> The Leicester meeting heard that the rising temperatures are causing
> ecological changes in the forests that ratchet up the warming still
> further. Vladimir Petko from the Russian Academy of Sciences Forest
> Research Institute in Krasnoyarsk says warm springs are triggering
> plagues of moths. “They can eat the needles of entire forest regions
> in one summer,” he says. The trees die and then usually succumb to
> forest fires that in turn destroy soil vegetation and accelerate the
> melting of permafrost, Petko says.
>
> In 2003 Siberia saw a record number of forest fires, losing 40,000
> square kilometres according to Balzter, who has analysed remote
> sensing images of the region. Similar changes are occurring in Alaska.
> According to Chapin, warming there has shortened the life cycle of the
> bark beetle from two years to one, causing huge infestations and
> subsequent fires, which destroyed huge areas of forest in 2004. “The
> current boreal forest zone could be so dried out by 2090 that the
> trees will die off and be replaced by steppe,” says Nadezhda
> Tchebakova, also at the institute in Krasnoyarsk.
>
> Melting permafrost in the boreal forests and further north in the
> Arctic tundra is also triggering the release of methane, a powerful
> greenhouse gas, from thick layers of thawing peat. First reports
> published exclusively in /New Scientist/ last year (13 August 2005, p
> 12) were recently confirmed by US scientists (/Nature/, vol 443, p 71).
>
> “Large amounts of greenhouse gases are currently locked in the
> permafrost and if released could accelerate the greenhouse effect,”
> says Balzter. Hansen’s paper concludes that the effects of this
> positive feedback could be huge. “In past eras, the release of methane
> from melting permafrost and destabilised sediments on continental
> shelves has probably been responsible for some of the largest warmings
> in the Earth’s history,” he says.
>
> “The release of methane from melting permafrost has been responsible
> for some of the largest warmings in history”
>
> We could be close to unleashing similar events in the 21st century,
> Hansen argues. Although the feedbacks should remain modest as long as
> global temperatures remain within the range of recent interglacial
> periods of the past million years, outside that range - beyond a
> further warming of about 1 �C - the feedbacks could accelerate. Such
> changes may become inevitable if the world does not begin to curb
> greenhouse gas emissions within the next decade, Hansen says.
>
> Meanwhile, another new study underlines that the boreal peat bogs,
> permafrost and pine forests are not just vital to the planet as a
> whole, they are major economic assets for the countries that host
> them. A detailed study of the northern boreal forests by environmental
> consultant Mark Anielski of Edmonton, Canada, puts the value of their
> “ecosystem services” at $250 billion a year, or $160 per hectare.
>
> “The value of the services this ecosystem performs is more than twice
> that of the resources taken from the region each year”
>
> These benefits include flood control, water purification and pest
> control provided by forest birds, plus income from wilderness tourism
> and meat from wildlife such as caribou. Anielski presented his
> findings to Canada’s National Forest Congress in Gatineau-Ottawa
> earlier this week.
>
> The value of these ecosystem services is more than twice that of
> conventional resources taken from the region each year, such as
> timber, minerals, oil and hydroelectricity, Anielski says. “If they
> were counted in Canadian inventories of assets, they would amount to
> roughly 9 per cent of our gross domestic product - similar in value to
> our health and social services.”
>
> You can add to that figure the value of having such a huge volume of
> carbon locked away. “The boreal region is like a giant carbon bank
> account,” he says. “At current prices in the European carbon emissions
> trading system, Canada’s stored carbon alone would be worth $3.7
> trillion.”
>
> And if Hansen is right that the carbon and methane stored in the
> boreal regions has the potential to transform the world into “another
> planet”, then the boreal region may be worth a great deal more than that

After writing “Biofuels are not the Answer”, I came across a petition on the Number 10 website calling on “the Prime Minister [to] acknowledge that biofuels are neither sustainable nor ecologically sound and stop promoting them in Parliament, and to the public, as being such.”

Please sign this petition.

We are forever being bombarded with apparently incredible correlations of various solar indices and climate. A number of them came up in the excoriable TGGWS mockumentary last month where they were mysteriously 'improved' in a number of underhand ways. But even without those improvements (which variously involved changing the axes, drawing in non-existent data, taking out data that would contradict the point etc.), the as-published correlations were superficially quite impressive. Why then are we not impressed?

To give you an idea, I'm going to go through the motions of constructing a new theory of political change using techniques that have been pioneered by a small subset of solar-climate researchers (references will of course be given). And to make it even more relevant, I'm going to take as my starting point research that Richard Lindzen has highlighted on his office door for many years:

That's right. Forget the economy or the war(s), the fortunes of the Republican party in the US Senate are instead tied closely to the sunspot cycle.

"Oh yes", the sceptics might say "but that's just a couple of cycles and doesn't use up-to-date numbers. What happens after 1986?"

Well, that is a little problematic, however, the good early correlation is obviously still important (r=0.52! 1960-1986) and so we should be able to refer to it over and over again without noting that it breaks down subsequently (cf. Svensmark, 2007 referring to Marsh and Svensmark (2000)). But more importantly, it just demonstrates that the theory needs a little adjustment.

Let's look at the second half of the record. Well, there's another strong correlation for that period as well (r=-0.63, 1988-2006). Only this time the correlation is inverted, but that shouldn't be surprising to anyone - solar-senator effects are complicated!

If we now put it all together, we can see that there is a reasonable match over the whole period.... well, except that break in the period 1984 and 1988 and, unfortunately, last year's elections didn't fit the pattern either. But 1984-1988 was Ronald Reagan's second term and clearly no theory of Republican senators can ignore that. We therefore propose that the 'Ronald Reagan second term phase shift' combined with the change of sign of the Hale solar magnetic cycle in 1986, obviously changed the dynamics. This kind of phase shift is frequently seen in solar studies (cf. Landscheidt and many others), where it is rarely taken as a sign that two time series with decadal spectral power are in fact completely independent. Finally, it is permissible to leave off the more recent data points (cf. TGGWS) for "graphical convenience". So after just a little work, we have managed to rescue the original theory to match a much longer amount of data:

Some readers may scoff and suggest that in the absence of any mechanism, these powerful correlations are numerological artifacts arrived at using post hoc fallacious reasoning that have no predictive capability. That might appear to be a valid argument. However the ultimate test will of course be experimental. On the basis of these intriguing results, we propose exposing Republican senators to varying levels of cosmic rays in a basement and monitoring their electability. Any refusal by the funding agencies or ethical review panels to support this would simply be confirmation that the political science establishment are scared of what this research would imply for their so-called "consensus".

Convincing, eh?

The data for sunspots and senators can, I'm sure, be manipulated even more effectively than I've done here. I've made no use of various lags or filters (which can be altered as you go along cf. Friis-Christensen and Lassen (1991)), or of partial detrending (cf. Marsh and Svensmark (2003)), or of splicing of unconnected data sets (cf. Svensmark and Friis-Christensen 1997, Nir Shaviv). More ideas could be taken from "New evidence for the Theory of the Stork" (Höfer et al, 2004)". A special RealClimate commendation for anyone who can do better!

Fiddling with figures while the Earth burns

The Sunday Times May 6, 2007

The latest initiatives to stop global warming won’t save us, James Lovelock tells Jonathan Leake

If you want to get some idea of what much of the Earth might look like in 50 years’ time then, says James Lovelock, get hold of a powerful telescope or log onto Nasa’s Mars website. That arid, empty, lifeless landscape is, he believes, how most of Earth’s equatorial lands will be looking by 2050. A few decades later and that same uninhabitable desert will have extended into Spain, Italy, Australia and much of the southern United States.

“We are on the edge of the greatest die-off humanity has ever seen,” said Lovelock. “We will be lucky if 20% of us survive what is coming. We should be scared stiff.”

Lovelock has delivered such warnings before, but this weekend they have a special resonance. Last week in Bangkok, Thailand, the world’s governments finalised this year’s third and final report from the Intergovernmental Panel on Climate Change (IPCC) setting out how humanity might save itself from the worst effects of climate change.

In it was a message of hope, albeit a faint one. The report set out a complex mix of political, economic and technological solutions. If they all worked, said the report, they could achieve huge cuts in the 25 billion tons of carbon dioxide (CO2) released by humanity into the air each year, thus keeping global temperature rises below 3C.

At the same time in Cologne, Germany, 4,000 sharp-suited bankers, lawyers and financial traders at Carbon Expo 2007 were congratulating themselves on the booming new markets in carbon credits that will, they boasted, save the world as well as making them rich.

“I have a dream,” Yvo de Boer, executive secretary of the United Nations Framework Convention on Climate Change, told the delegates. He set out his belief that carbon trading will help stabilise greenhouse gas emissions and aid developing countries by transferring £50 billion a year to these nations from the First World to support green development.

For Lovelock, however, such dreams are dangerous nonsense on a par with a drowning man clutching at straws. “It’s all ridiculous,” he sighed. “These new markets do some good in that they generate wealth and keep these people employed, but they and the IPCC are just raising false hopes. We have done too much damage to the world and now it is changing too fast for us to make much difference.”

Lovelock’s view is that the world has two stable states: the “icehouse”, when ice covers both poles, sometimes extending far into lower latitudes in the form of ice ages; and the “greenhouse”, when all the ice melts. Both have already happened many times in the Earth’s history.

“Human outpourings of greenhouse gases have flicked the switch that turns the world from its colder to its warm state – and it is probably too late to stop it,” he said. “The warming impact of the carbon we have already released is such that the Earth has taken over and our greenhouse gas emissions are being amplified by nature itself.”

Lovelock believes that the transformation is happening far too fast for humanity to tackle, especially in a world that remains committed to economic growth and whose 6.5 billion population is predicted to reach more than 9 billion by mid-century.

For evidence, he points to Siberia where the melting of the permafrost, already widely reported in scientific literature, will enable bacteria to decompose organic matter that has accumulated in the soil over tens of millions of years – potentially releasing billions more tons of CO2 “I have just come back from Norway where the temperatures are even further above normal than Britain’s. The climate is changing every year now. Everyone can see it – as in this very warm April. By mid-century the heatwave [in Europe] that killed 20,000 people in 2003 will be a cool summer by comparison.”

At first sight Lovelock’s predictions seem wildly at odds with the IPCC’s reports, but in many ways the only difference is in the vividness of the language. “The progressive acidification of oceans due to increasing atmospheric carbon dioxide is expected to have negative impacts on marine shell-forming organisms (ie corals) and their dependent species,” said the IPCC report detailing the impacts of climate change – its careful language draining the drama from a warning that vast tracts of the ocean may turn so acidic that little life will be left in them.

It added: “At lower latitudes, especially seasonally dry and tropical regions, crop productivity is projected to decrease for even small local temperature increases (1-2C), which would increase risk of hunger.” What these measured tones imply, warns Lovelock, is that millions – perhaps hundreds of millions – of people living in equatorial lands will be forced from their homes, with most of them heading northwards. “The world will face mass shortages of food and water. That will lead to wars and the effective clearance of vast areas of land as the deserts spread,” he said.

Lovelock’s reputation as a scientific seer was founded four decades ago when he published his Gaia hypothesis. His idea, that the Earth’s chemistry, climate and life were all closely linked into a kind of self-sustaining system, is now received wisdom. It has become clear that the first life forms on Earth transformed its early climate and atmosphere, generating the oxygen that allowed life to evolve – eventually into us.

What’s more, that process continues. Oxygen is a reactive gas that would vanish from the atmosphere were it not for the plankton, and plants that keep topping it up.

Lovelock’s warnings may seem remote (and he hasn’t always been proved right) but with Britain basking in record spring heat he says our scepticism about the damage we can expect from global warming is understandable. “Britain and Scandinavia are becoming green oases. In 2050 or soon after, most of the world may be scrub and desert and most of the oceans will be denuded of life, but temperatures here will remain very tolerable. The downside of that is that we risk becoming like a lifeboat with millions of refugees trying to settle here.”

He is not alone in predicting a huge northwards shift in human populations: in his new book, How the World will Change with Global Warming, Professor Trausti Valsson, an Icelandic academic, predicts how population centres will move north.

“The Arctic ice cap is melting. When it goes it will open up new shipping routes, new fishing grounds and new oil fields,” said Valsson. “The Arctic Ocean will become the new Mediterranean with Siberia and Canada as the centres for human culture and civilisation.”

Lovelock is fond of recounting how, on a recent lecture tour of America, he was accosted by earnest academics seeking advice on whereabouts in Canada they should buy their second homes.

Behind such comic anecdotes, however, lies the grim possibility that billions of people face a miserable life and death as humanity finds a new equilibrium with the Earth. At 87 Lovelock acknowledges that he is unlikely to be one of them. His concern is for the generations represented by his nine grandchildren. “What we have lived through, the 20th century, has been like a great party. Adults now have had the best time humanity has ever had. Now the party is over and the Earth is reckoning up.”

Six steps to hell - Mark Lynas

By the end of the century, the Earth could be more than 6C hotter than
it is today, according to the Intergovernmental Panel on Climate
Change. We know that would be bad news - but just how bad? How big a
rise will it take for the Alps to melt, the oceans to die and desert
to conquer Europe and the Americas? Mark Lynas sifted through
thousands of scientific papers for his new book on global warming.
This is what the research told him …

Monday April 23, 2007 The Guardian

Nebraska isn’t at the top of most tourists’ to-do lists. However, this
dreary expanse of impossibly flat plains sits in the middle of one of
the most productive agricultural systems on Earth. Beef and corn
dominate the economy, and the Sand Hills region - where low, grassy
hillocks rise up from the flatlands - has some of the best cattle
ranching in the whole US. But scratch beneath the grass and you will
find, as the name suggests, not soil but sand. These innocuous-looking
hills were once desert, part of an immense system of sand dunes that
spread across the Great Plains from Texas in the south to the Canadian
prairies in the north. Six thousand years ago, when temperatures were
about 1C warmer than today in the US, these deserts may have looked
much as the Sahara does today. As global warming bites, the western US
could once again be plagued by perennial drought - devastating
agriculture and driving out human inhabitants on a scale far larger
than the 1930s “Dustbowl” exodus.

On the other side of the Atlantic, today’s hottest desert could be
seeing a wetter future in the one-degree world. At the same time as
sand dunes were blowing across the western US, the central Sahara was
a veritable Garden of Eden as rock paintings of elephants, giraffes
and buffalo, also dating from 6,000 years ago, attest. On the borders
of what is today Chad, Nigeria and Cameroon, the prehistoric Lake
Mega-Chad spread over an area only slightly smaller than the Caspian
Sea does now. Could a resurgent north African monsoon drive rainfall
back into the Sahara in a one-degree world? Models suggest it could.
Also in Africa, Mount Kilimanjaro will be losing the last of its snow
and ice as temperatures rise, leaving the entire continent ice-free
for the first time in at least 11,000 years. The Alps, too, will be
melting, releasing deadly giant landslides as thawing permafrost
removes the “glue” that holds the peaks together. In the Arctic,
temperatures will rise far higher than the one-degree global average,
continuing the rapid decline in sea ice that scientists have already
observed. This spells bad news for polar bears, walruses and ringed
seals - species that are effectively pushed off the top of the planet
as warming shrinks cold areas closer and closer to the pole.

Indeed, it is the ecological effects of warming that may be most
apparent at one degree. Critically, this temperature rise may wipe out
the majority of the world’s tropical coral reefs, devastating marine
biodiversity. Most of the Great Barrier Reef will be dead.

In the highly unlikely event that global warming deniers prove to be
right, we will still have to worry about carbon dioxide, because it
dissolves in the oceans and makes them more acidic. Even with
relatively low emissions, large areas of the southern oceans and parts
of the Pacific will within a few decades become toxic to organisms
with calcium carbonate shells, for the simple reason that the acidic
seawater will dissolve them. Many species of plankton - the basis of
the marine food chain and essential for the sustenance of higher
creatures, from mackerel to baleen whales - will be wiped out, and the
more acidic seawater may be the knockout blow for what remains of the
world’s coral reefs. The oceans may become the new deserts as the
world’s temperatures reach 2C above today’s.

Two degrees may not sound like much, but it is enough to make every
European summer as hot as 2003, when 30,000 people died from
heatstroke. That means extreme summers will be much hotter still. As
Middle East-style temperatures sweep across Europe, the death toll may
reach into the hundreds of thousands. The Mediterranean area can
expect six more weeks of heatwave conditions, with wildfire risk also
growing. Water worries will be aggravated as the southern Med loses a
fifth of its rainfall, and the tourism industry could collapse as
people move north outside the zones of extreme heat.

Two degrees is also enough to cause the eventual complete melting of
the Greenland ice sheet, which would raise global sea levels by seven
metres. Much of the ice-cap disappeared 125,000 years ago, when global
temperatures were 1-2C higher than now. Because of the sheer size of
the ice sheet, no one expects this full seven metres to come before
the end of the century, but a top Nasa climate scientist, James
Hansen, is warning that the mainstream projections of sea level rise
(of 50cm or so by 2100) could be dangerously conservative. As if to
underline Hansen’s warning, the rate of ice loss from Greenland has
tripled since 2004.

This melting will also continue to affect the world’s mountain ranges,
and in Peru all the glaciers will disappear from the Andean peaks that
currently supply Lima with water. In California, the loss of snowpack
from the Sierra Nevada - three-quarters of which could disappear in
the two-degree world - will leave cities such as Los Angeles
increasingly thirsty during the summer. Global food supplies,
especially in the tropics, will also be affected but while two degrees
of warming will be survivable for most humans, a third of all species
alive today may be driven to extinction as climate change wipes out
their habitat.

Scientists estimate that we have at best 10 years to bring down global
carbon emissions if we are to stabilise world temperatures within two
degrees of their present levels. The impacts of two degrees warming
are bad enough, but far worse is in store if emissions continue to
rise. Most importantly, 3C may be the “tipping point” where global
warming could run out of control, leaving us powerless to intervene as
planetary temperatures soar. The centre of this predicted disaster is
the Amazon, where the tropical rainforest, which today extends over
millions of square kilometres, would burn down in a firestorm of epic
proportions. Computer model projections show worsening droughts making
Amazonian trees, which have no evolved resistance to fire, much more
susceptible to burning. Once this drying trend passes a critical
threshold, any spark could light the firestorm which destroys almost
the entire rainforest ecosystem. Once the trees have gone, desert will
appear and the carbon released by the forests’ burning will be joined
by still more from the world’s soils. This could boost global
temperatures by a further 1.5=BAC - tippping us straight into the
four-degree world.

Three degrees alone would see increasing areas of the planet being
rendered essentially uninhabitable by drought and heat. In southern
Africa, a huge expanse centred on Botswana could see a remobilisation
of old sand dunes, much as is projected to happen earlier in the US
west. This would wipe out agriculture and drive tens of millions of
climate refugees out of the area. The same situation could also occur
in Australia, where most of the continent will now fall outside the
belts of regular rainfall.

With extreme weather continuing to bite - hurricanes may increase in
power by half a category above today’s top-level Category Five - world
food supplies will be critically endangered. This could mean hundreds
of millions - or even billions - of refugees moving out from areas of
famine and drought in the sub-tropics towards the mid-latitudes. In
Pakistan, for example, food supplies will crash as the waters of the
Indus decline to a trickle because of the melting of the Karakoram
glaciers that form the river’s source. Conflicts may erupt with
neighbouring India over water use from dams on Indus tributaries that
cross the border.

In northern Europe and the UK, summer drought will alternate with
extreme winter flooding as torrential rainstorms sweep in from the
Atlantic - perhaps bringing storm surge flooding to vulnerable
low-lying coastlines as sea levels continue to rise. Those areas still
able to grow crops and feed themselves, however, may become some of
the most valuable real estate on the planet, besieged by millions of
climate refugees from the south.

At four degrees another tipping point is almost certain to be crossed;
indeed, it could happen much earlier. (This reinforces the
determination of many environmental groups, and indeed the entire EU,
to bring us in within the two degrees target.) This moment comes as
the hundreds of billions of tonnes of carbon locked up in Arctic
permafrost - particularly in Siberia - enter the melt zone, releasing
globally warming methane and carbon dioxide in immense quantities. No
one knows how rapidly this might happen, or what its effect might be
on global temperatures, but this scientific uncertainty is surely
cause for concern and not complacency. The whole Arctic Ocean ice cap
will also disappear, leaving the North Pole as open water for the
first time in at least three million years. Extinction for polar bears
and other ice-dependent species will now be a certainty.

The south polar ice cap may also be badly affected - the West
Antarctic ice sheet could lift loose from its bedrock and collapse as
warming ocean waters nibble away at its base, much of which is
anchored below current sea levels. This would eventually add another
5m to global sea levels - again, the timescale is uncertain, but as
sea level rise accelerates coastlines will be in a constant state of
flux. Whole areas, and indeed whole island nations, will be submerged.

In Europe, new deserts will be spreading in Italy, Spain, Greece and
Turkey: the Sahara will have effectively leapt the Straits of
Gibraltar. In Switzerland, summer temperatures may hit 48C, more
reminiscent of Baghdad than Basel. The Alps will be so denuded of snow
and ice that they resemble the rocky moonscapes of today’s High Atlas
- glaciers will only persist on the highest peaks such as Mont Blanc.
The sort of climate experienced today in Marrakech will be experienced
in southern England, with summer temperatures in the home counties
reaching a searing 45C. Europe’s population may be forced into a
“great trek” north.

To find out what the planet would look like with five degrees of
warming, one must largely abandon the models and venture far back into
geological time, to the beginning of a period known as the Eocene.
Fossils of sub-tropical species such as crocodiles and turtles have
all been found in the Canadian high Arctic dating from the early
Eocene, 55 million years ago, when the Earth experienced a sudden and
dramatic global warming. These fossils even show that breadfruit trees
were growing on the coast of Greenland, while the Arctic Ocean saw
water temperatures of 20C within 200km of the North Pole itself. There
was no ice at either pole; forests were probably growing in central
Antarctica.

The Eocene greenhouse event fascinates scientists not just because of
its effects, which also saw a major mass extinction in the seas, but
also because of its likely cause: methane hydrates. This unlikely
substance, a sort of ice-like combination of methane and water that is
only stable at low temperatures and high pressure, may have burst into
the atmosphere from the seabed in an immense “ocean burp”, sparking a
surge in global temperatures (methane is even more powerful as a
greenhouse gas than carbon dioxide). Today vast amounts of these same
methane hydrates still sit on subsea continental shelves. As the
oceans warm, they could be released once more in a terrifying echo of
that methane belch of 55 million years ago. In the process, moreover,
the seafloor could slump as the gas is released, sparking massive
tsunamis that would further devastate the coasts.

Again, no one knows how likely this apocalyptic scenario is to unfold
in today’s world. The good news is that it could take centuries for
warmer water to penetrate down to the bottom of the oceans and release
the stored methane. The bad news is that it could happen much sooner
in shallower seas that see a stronger heating effect (and contain lots
of methane hydrate) such as in the Arctic. It is also important to
realise that the early Eocene greenhouse took at least 10,000 years to
come about. Today we could accomplish the same feat in less than a
century.

If there is one episode in the Earth’s history that we should try
above all not to repeat, it is surely the catastrophe that befell the
planet at the end of the Permian period, 251 million years ago. By the
end of this calamity, up to 95% of species were extinct. The
end-Permian wipeout is the nearest this planet has ever come to
becoming just another lifeless rock drifting through space. The
precise cause remains unclear, but what is undeniable is that the
end-Permian mass extinction was associated with a super-greenhouse
event. Oxygen isotopes in rocks dating from the time suggest that
temperatures rose by six degrees, perhaps because of an even bigger
methane belch than happened 200 million years later in the Eocene.

Sedimentary layers show that most of the world’s plant cover was
removed in a catastrophic bout of soil erosion. Rocks also show a
“fungal spike” as plants and animals rotted in situ. Still more
corpses were washed into the oceans, helping to turn them stagnant and
anoxic. Deserts invaded central Europe, and may even have reached
close to the Arctic Circle.

One scientific paper investigating “kill mechanisms” during the
end-Permian suggests that methane hydrate explosions “could destroy
terrestrial life almost entirely”. Acting much like today’s fuel-air
explosives (or “vacuum bombs”), major oceanic methane eruptions could
release energy equivalent to 10,000 times the world’s stockpile of
nuclear weapons.

Whatever happened back then to wipe out 95% of life on Earth must have
been pretty serious. And while it would be wrong to imagine that
history will ever straightforwardly repeat itself, we should certainly
try and learn the lessons of the distant past. If they tell us one
thing above all, it is this: that we mess with the climatic thermostat
of this planet at our extreme - and growing - peril.