For people in their 30s, climate change has already reshaped the world into which they were born.
By the time they reach retirement, the changes will be far more dramatic and perhaps life-threatening on a massive scale, an authoritative UN study will say this week.
Today, the Intergovernmental Panel on Climate Change (IPCC), a network of more than 2,000 scientists, will open a five-day meeting in Brussels, Belgium, to finalize a report on how warming will affect the globe and whether humans can do anything about it.
The panel will paint a bleak picture of increasing poverty, paucity of drinking water, melting glaciers and polar ice caps, and a host of vanishing species by mid-century unless action is taken to curb emissions of carbon dioxide and other heat-trapping gases.
Among the gloomy forecasts, the report predicts that glaciers in the Himalayas, the world's highest mountain range, will melt away, affecting hundreds of millions of people.
"If current warming rates are maintained, Himalayan glaciers could decay at very rapid rates, shrinking from the present 500,000 square kilometers to 100,000 square kilometers by 2030s," according to a draft technical summary.
Some regions, like parts of North America and northern Europe, will see some benefits, at least in the short term, from longer growing seasons and milder winters.
Even the most optimistic forecasts say the climate will continue to change and the planet will be irrevocably damaged. The question is, how much?
"We are going into a realm the Earth has not seen for a very long time... over the past 800,000 years," said Camille Parmesan, a University of Texas biologist who has studied the effects of climate change on wildlife and was a reviewer of the upcoming report.
Guideline for governments
Policymakers will go over the IPCC document line-by-line this week before unveiling the final text on Friday. It will then become a guideline for governments to determine policies and draft legislation.
About 285 delegates from 124 countries are attending, along with more than 50 of the scientists who compiled the report and dozens of observers from nongovernment, mostly environmental, organizations.
The closed-door talks are likely to focus on predictions of how many people will be at high risk from changing ecosystems and water cycles, and whether such specific weather events like Hurricane Katrina should be attributed to global warming.
"Do you use examples? And do you use ones that are relatively positive or highly negative?" said Rik Leemans, a co-author from Wageningen University in the Netherlands. "You can tone it down or strengthen it by including examples, and that's always an issue in these discussions."
The summary's final wording must be adopted by consensus among the diplomats, with the approval of the scientists.
While there may be editing for the sake of nuance, the underlying premise of the draft report will not change. "A decade ago, climate impacts were largely hypothetical," said James J. McCarthy, a Harvard University oceanographer who was a main author of the 2001 IPCC report. "That's no longer a question."
It is the second of four reports by the IPCC. The first, issued in February, updated the science of climate change, concluding with near certainty that global warming is caused by human behavior.
That report galvanized the European Union to adopt an ambitious goal of reducing carbon emissions by at least 20 percent from 1990 levels by 2020.
The IPCC's work will be presented at a summit in June of leaders from the world's richest countries, including US President George W. Bush whose administration has declined to take coordinated action with other nations to limit greenhouse gases.
The latest report was six years in the making. Since the IPCC's 2001 assessment, knowledge about climate change has become more precise, and studies have tracked specific shifts on the ground to changing temperatures and weather patterns.
"Many natural systems on all continents and in some oceans are being affected by regional climate changes, particularly temperature increases," reads the final draft.
Parmesan said storms and floods have become more severe in some places, coastlines have eroded and deserts have expanded. Diseases common in the tropics have spread. In the Northern Hemisphere, spring is coming an average two weeks earlier, disrupting bird migrations and causing flowers and trees to bloom too early. At least 70 species have become extinct so far because of global warming, Parmesan said in a telephone conference with reporters.
'Highway to extinction'
The report will offer stark warnings for the future.
Within 25 years, hunger and death from diarrhea will threaten poor countries where crops fail and water becomes more scarce. Later in the 21st Century, warmer seas will likely destroy coral reefs and the fish that feed off them, and may lead to the poisoning of shellfish. Tens of millions of people in coastal cities and river basins will likely be affected by flooding, and fresh water supplies will likely be inundated with salt water from sea surges. Small islands will probably be submerged by rising sea levels. Beetles and other pests are expected to infest forests even more, with forest and wild fires more frequent and widespread.
University of Victoria climate scientist Andrew Weaver said the chart of results from various temperature levels is "a highway to extinction, but on this highway there are many turnoffs. This is showing you where the road is heading. The road is heading toward extinction."
Weaver is one of the lead authors of the first report in February.
While humanity will survive, hundreds of millions, maybe billions of people may not, according to the chart if the worst scenarios happens.
The report says global warming has already degraded conditions for many species, coastal areas and poor people. With a more than 90 percent level of confidence, the scientists in the draft report say man-made global warming "over the last three decades has had a discernible influence on many physical and biological systems."
And as the world's average temperature warms from 1990 levels, the projections get more dire. Add 1 degree centigrade and between 400 million and 1.7 billion extra people cannot get enough water, some infectious diseases and allergenic pollens rise, and some amphibians go extinct. But the world's food supply, especially in northern areas, could increase. That is the likely outcome around 2020, according to the draft.
Add another 1.8 degrees and as many as 2 billion people could be without water and about 20 percent to 30 percent of the world's species near extinction. Also, more people start dying because of malnutrition, disease, heat waves, floods and droughts all caused by global warming. That would happen around 2050, depending on the level of greenhouse gases from the burning of fossil fuels.
At the extreme end of the projections, the chart predicts: "Up to one-fifth of the world population affected by increased flood events... 1.1 to 3.2 billion people with increased water scarcity... "major extinctions around the globe."
Impact of climate change on different regions
Projected increases in temperatures and changes in precipitation "will increase the risk of hunger in Asia, especially in developing countries".
If current warming rates are maintained, Himalayan glaciers could shrink to 100,000 square kilometers by the 2030s from 500,000 square kilometers now. That would disrupt river flows and bring more rock avalanches.
Around 30 percent of Asian coral reefs are expected to be lost in the next 30 years due to climate change and other factors.
Between 120 million and 1.2 billion people are likely to experience more water shortages by the 2020s.
A 1 meter rise in sea level far above the 18-59 centimeter gain projected for 2100 would lead to widespread flooding in deltas such as the Mekong and Red Rivers. Flooding with a 1 meter rise in sea level could affect 3-5.5 million people in the delta, and 4 million in the Red River delta.
The annual per capita availability of freshwater in India is expected to drop from around 1,900 cubic meters to 1,000 by 2025 due to population growth and climate change.
Falls in crop yields are suggested for parts of Asia.
The percentage of river basin areas with severe water stress is expected to increase from 19 percent to 34-36 percent by the 2070s.
Millions of people are likely to live in watersheds with shortages in western Europe.
Under scenarios of a fast rise in global temperatures, an extra 2.5 million people a year will be affected by coastal flooding by the 2080s.
By the 2070s, hydropower potential for Europe is expected to decline overall by 6 percent, ranging from a 20-50 percent decrease in the Mediterranean region to a 15-30 percent increase in Northern and Eastern Europe.
A large percentage of European flora could become vulnerable, endangered, critically endangered or extinct under a range of scenarios.
By 2050, crops are expected to show a northward expansion. In northern Europe, wheat yields may gain by 8 to 25 percent by 2050. But in the south, yields may range from a fall of 8 percent to a gain of 22 percent by 2050.
Forested area is likely to increase in the north and decrease in the south, with a redistribution of species. Forest fire risk is virtually certain to increase greatly in southern Europe.
Small alpine glaciers will disappear, while larger glaciers will suffer a volume reduction of between 30 to 70 percent by 2050.
Tourism to the Mediterranean might fall in summer and increase in spring and autumn.
A rapid shutdown of the Gulf Stream bringing warm waters northwards across the Atlantic to Europe viewed as a low probability could have severe impacts such as cutting crop production, more cold-related deaths, and a shift in populations south.
Population growth, rising property values and continued investment increase the vulnerability of coastal regions. Any rise in destructiveness of coastal storms is very likely to bring "dramatic increases" in losses from severe weather and storm surges.
Sea level rises, tidal surges and flooding have the "potential to severely affect transportation and infrastructure along the Gulf, Atlantic and northern coasts."
Severe heatwaves are likely to worsen over parts of the United States and Canada.
Ozone related deaths are projected to increase by 4.5 percent from the 1990s to the 2050s.
Projected warming in the western mountains is likely to cause large decreases in snowpack, earlier snowmelt and more winter rains by mid-century.
Climate change is likely to increase forest production. But by the second half of the century, the dominant impacts will be disruptions from pests and fires. Forest areas burnt each summer in Canada could rise by between 74 and 118 percent by 2100 compared to now.
Glaciers in the tropical Andes are very likely to disappear over the next 15 years, reducing water availability and hydropower generation in Bolivia, Peru, Colombia and Ecuador.
Any decline in rainfall in semi-arid regions of Argentina, Brazil and Chile is likely to lead to severe water shortages.
By the 2020s, between 7 and 77 million people are likely to suffer from a lack of adequate water supplies.
A rise in sea level, weather and climatic variability are very likely to have impacts on low-lying areas, buildings and tourism, mangroves, coral reefs and the location of fish stocks off Peru and Chile.
Temperature increases of 2 C and decreases in soil water would turn eastern parts of Amazonia to savannah from tropical forest. In turn, that could threaten many species.
The frequency and intensity of hurricanes in the Caribbean might increase.
Many ecosystems are likely to be altered by 2020. Among the most vulnerable are the Great Barrier Reef, south-western Australia, Kakadu wetlands, rainforests and mountain areas.
Water security problems are very likely to increase by 2030 in southern and eastern Australia, and parts of eastern New Zealand away from major rivers. In Australia, there could be a 10-25 percent reduction in river flow in the Murray-Darling basin by 2050.
Development of coastal regions could lead to property coming under threat from rising sea levels. By 2050 there is likely to be loss of high-value land, faster road deterioration and degraded beaches.
In southeast Australia, the frequency of days when bush fires threaten is likely to rise by between 4 and 25 percent by 2020.
Increased temperatures and demographic changes are likely to increase peak energy demand in summer which could lead to black-outs.
Farm production is likely to decline over much of southern and eastern Australia and parts of eastern New Zealand due to increased drought and fire. If enough water is available, longer growing seasons and less risk of frost are likely to aid farming in much of New Zealand and parts of southern Australia.
In south and west New Zealand, growth rates of economically important plantation crops are likely to increase.
The elderly will be at risk from heatwaves, with an extra 3,200-5,200 deaths on average per year by 2050.
Reductions in the area suitable for agriculture, the length of growing seasons and yield potential, are likely to lead to increased risk of hunger.
An increase of 5-8 percent (60-90 million hectares) of arid and semi-arid land in Africa is projected by the 2080s.
Current stress on water in many areas of Africa is likely to increase, with floods and droughts.
Any changes in the productivity of large lakes are likely to affect local food supplies.
Ecosystems in Africa are likely to experience dramatic changes with some species facing possible extinctions.
Major delta regions with large populations, such as the Nile and Niger rivers, will be threatened by sea level rises.
Source: China Daily/agencies