Saturday, February 03, 2007

Fourth report on climate change by IPCC

Worse than we thought

• Report warns of 4C rise by 2100
• Floods and food and water shortages likely

David Adam in Paris

Guardian February 3, 2007

The world's scientists yesterday gave their starkest warning yet that a failure to cut greenhouse gas emissions will bring devastating climate change within a few decades.
Average temperatures could increase by as much as 6.4C by the end of the century if emissions continue to rise, with a rise of 4C most likely, according to the final report of an expert panel set up by the UN to study the problem. The forecast is higher than previous estimates, because scientists have discovered that Earth's land and oceans are becoming less able to absorb carbon dioxide.
An average global temperature rise of 4C would wipe out hundreds of species, bring extreme food and water shortages in vulnerable countries and cause catastrophic floods that would displace hundreds of millions of people. Warming would be much more severe towards the poles, which could accelerate melting of the Greenland and west Antarctic ice sheets.
The report, from the Intergovernmental Panel on Climate Change (IPCC), is written by hundreds of scientists across the world and has been approved by every government. It leaves little room for doubt that human activity is to blame. Achim Steiner, executive director of the UN Environment Programme, said: "February 2 2007 may be remembered as the day the question mark was removed from whether people are to blame for climate change."
The report itself said human activity was "very likely" to be responsible for most of the observed warming in recent decades, which means the scientists are 90% sure.
The new warning comes as world governments face increasing pressure to agree a new global deal to reduce emissions.
Susan Solomon, the co-chair of the IPCC working group that prepared the report, said: "If we keep emitting greenhouse gases at current rates we will see bigger changes this century than we did in the previous century. The amount of warming will depend on choices that human beings make."
The previous IPCC report, in 2001, said that failure to act could bring global warming of up to 5.8C by 2100.
Dr Solomon said yesterday's predictions painted a gloomier picture because scientists have discovered feedbacks in the global carbon cycle that are adding to the amount of carbon dioxide in the atmosphere. Early estimates say this would be enough to raise temperatures by at least another 1C by 2100.
A 4C rise or higher this century would see the world warm almost as much in 100 years as it did during the 15,000 years since the end of the last ice age.
The IPCC panel stressed that such an outcome was not inevitable. A significant switch to "clean and resource efficient technologies" would cut expected temperature rises by half. But even their most optimistic scenario would see a likely increase in temperature of 2.4C over pre-industrial levels by 2100. The EU has defined any rise over 2C as "dangerous".
David Miliband, the environment secretary, said the report was "another nail in the coffin of the climate change deniers and represents the most authoritative picture to date, showing that the debate over the science of climate change is well and truly over". He added: "What's now urgently needed is the international political commitment to take action. This has been absent so far."
What +4C will mean
Loss of food production
Droughts. African crops slump 15% to 35%. Global production falls 10%
Increased flooding
Sea levels rise by up to 59cm. Bangladesh and Vietnam worst hit, along with coastal cities such as London, New York, Tokyo, Hong Kong, Calcutta and Karachi. 1.8m people at risk from coastal flooding in Britain alone
Melting ice
Half the Arctic tundra at risk. Europe loses 80% of alpine glaciers. West Antarctic ice sheet and the Greenland ice sheet start to melt
More disease
Mosquitoes thrive, exposing 80 m more people to malaria in Africa; 2.5bn more exposed to dengue fever
Loss of land species
20-50% of land species threatened with extinction
Water shortages
Fresh water availability halved in southern Africa and Mediterranean
Hurricanes more powerful Wind strengths increasing 15-25%. Great damage to infrastructure

Fossil fuel and land use behind CO2 rise

Hilary Osborne

Guardian February 2, 2007

The first volume of the fourth assessment report by the Intergovernmental Panel on Climate Change (IPCC) has been almost three years in the writing and brings together the work of 600 writers from 40 countries. More than 620 experts have reviewed the findings, and representatives of 113 governments have read and revised the key points.
The report assesses our current knowledge of climate change and the reasons behind it, looks at how the climate has already changed and how a range of different scenarios may have an impact in the future.
Story so far
According to the report there is evidence that the higher temperatures of the last half century are unusual compared with the at least the previous 1,300 years. As greenhouse gas levels have risen so have temperatures - global average air and ocean temperatures have been increasing and there has been widespread melting of snow and ice.
Eleven of the last 12 years have ranked among the 12 warmest years since records began in 1850, and as a result, the 100-year trend in temperatures has been adjusted upwards since the 2001 report, from an increase of 0.6C to 0.74C by the end of 2005. Much of the increase was recorded over the last 50 years, when the temperature increased by an average of 0.13C a decade - almost twice as fast as over the previous 100 years.
Research shows that the ocean has been absorbing more than 80% of the extra heat, causing water to expand and sea levels to rise. Between 1961 and 2003, the IPCC says, the global average sea level rose by an average of 1.8mm a year. And between 1993 and 2003 it was rising at a rate of 3.1mm a year. Whether this is a blip in the long-term trend, or an increase in the long-term outlook is unclear, but scientists are confident that sea levels rose much more quickly last century than in the 1800s.
Average Arctic temperatures have increased at almost twice the global average rate over the past 100 years, and the ice has shrunk by 2.7% each decade. Since 1900, the area covered by frozen ground has decreased by about 7%.
Elsewhere, more intense and longer droughts have been seen over wider areas since the 1970s, particularly in the tropics and sub-tropics, and in the North Atlantic there has been an increase in the incidence of typhoons and hurricanes.
The IPCC says the warming of the atmosphere and the ocean, together with the loss of ice, support the conclusion that it is very likely that climate change over the past 50 years is not down to natural causes alone and that it is extremely likely there were human causes.
The levels of greenhouse gases in the atmosphere have increased markedly since 1750 and now far exceed the levels before the industrial revolution. Human use of fossil fuels, and changes in land use, are the main drivers behind the increase in carbon dioxide levels, while agriculture has increased levels of methane and nitrous oxide.
The IPCC says levels of carbon dioxide increased from a pre-industrial level of 280 parts per million (ppm) to 379ppm in 2005 - far exceeding the natural range over the last 650,000 years, which has been measured as between 180ppm and 300ppm.
Most worryingly, the levels have increased more quickly over the past 10 years than they have since 1960 when scientists first began to record the increase.
What happens next
Scientists were able to draw from a larger number of simulations and models than when putting together the 2001 report - and the new data has caused them to suggest even more gloomy scenarios. It is now "virtually certain" that there will be fewer cold days and nights and more frequent hot days and nights over land.
Even if greenhouse gases were still at 2000 levels, the IPCC says over the next two decades global temperature rises of 0.2C a decade would be expected. With emissions set to rise its is "very likely" the increase will be twice that - 0.4C higher by 2030 - and that changes in the climate will be greater than those seen in the 20th century.
By the end of this century, temperatures could be between 1.8C and 4C higher than in 1999, although some of the scenarios considered by the IPCC suggested a rise of as much as 6.4C. In 2001, using a different methodology, scientists predicted an increase of 1.4 to 5.8C.
Warming of just 1.8C over the century could be achieved by moving rapidly towards a service and information economy, with reductions in the materials people use and the introduction of clean, efficient technologies, the IPCC says. There would have to be an emphasis on global solutions to economic, social and environmental sustainability.
The worst-case scenario, with warming of 4C, would be the result of rapid economic growth, a global population that peaks in the middle of the century and the rapid introduction of new technologies, but continued reliance on fossil fuels. A switch to non-fossil fuels would instantly cut the predicted temperature rise to 2.4C.
The scenarios for sea levels suggest a rise of between 18cm and 59cm over the same period, with the events that could lead to the highest temperatures also leading to the biggest increase in sea levels.
However, the predictions don't take into account the extra water that will enter the oceans as ice caps melt, so the real figures could be much higher. The last time the polar regions were significantly warmer than now was around 125,000 years ago, and the meltdown which that caused led to a 4-6m rise in sea levels.
If the ice flow in Greenland and Antarctica were to melt at a rate directly in proportion with the predicted rise in temperatures, the upper estimate for the sea level rise would increase by 10-20cm, and the IPCC says larger increases could not be excluded. It says knowledge of the impact of melting ice is "too limited" for a conclusion to be reached.
The report says snow cover will contract and sea ice will shrink in both the Arctic and Antarctic, and that late-summer sea ice may disappear entirely in the Arctic by the latter part of this century.
It is very likely that heat waves and heavy rain will become more frequent, and tropical cyclones will become more intense.
Because the oceans will be unable to take up carbon dioxide at the same rate as in the past, atmospheric greenhouse gas levels will increase more rapidly. To stabilise carbon levels at 450ppm, emissions would have to be reduced by around a third over the course of the century, the IPCC says.
The CO2 that has already been produced will continue to contribute to warming and sea level rise for more than a millennium.

A Summary is on http://www.ipcc.ch/SPM2feb07.pdf

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