The warming (and cooling) of the Earth have been the subject of scientific research for centuries, but the first precise measurements of what we now call global warming were taken almost 50 years ago on Hawaii's Big Island by a researcher at the University of California's Scripps Institution of Oceanography.

Dave Keeling, a keen hiker, preferred research topics that meant he could work outdoors, and monitoring carbon dioxide (CO2) in the open air fit his bill. In 1958, he lugged an infrared gas analyzer two miles to a weather station at the top of Mauna Loa, the Big Island's second highest mountain-a location known to have some of the cleanest air on the planet.

His findings over the next 40 years, plotted on a graph now known as the Keeling curve, showed a steady increase in levels of CO2 in the atmosphere, over and above the regular seasonal cycle. The measurements, now being taken by Keeling's son, Ralph, represent one of the most important geophysical records made and challenged the commonly held view that the oceans would readily absorb any excess CO2 from the atmosphere produced by the burning of fossil fuels and other industrial activities. (It's said that during the early 1990s, the only scientific data on display in the White House was one of Keeling's graphs.)

Today, the phenomenon that Keeling first charted has become one of the most hotly debated, divisive, and controversial topics on the planet. And in order to stave off the dire effects that global warming promises to deliver, it will also have to become the opportunity for unity and global collaboration on an unprecedented level. Here's a look at the science and politics around this buzzword.

Why does CO2 matter?
CO2, along with other gases, such as methane (CH4)and chlorofluorocarbons (CFCs), are called greenhouse gases because they trap the sun's radiation within the lower part of our atmosphere, the troposphere. These gases allow radiation from the sun to warm the planet but block it as it is radiated back off the surface, forming a virtual blanket, or greenhouse effect, around the globe. And the more greenhouse gases we add, the more our planet warms.

But that's not the end of the story. As CO2 and other greenhouse gases build up, a series of chain-reaction effects occur. Known as "positive feedbacks," they further amplify the global warming. For example, as more water evaporates from our seas and oceans, this magnifies the impact of the CO2 increase.

The average surface temperature of the Earth rose by close to 0.8°C (about 1.4°F) during the last century. And by examining the evidence found in tree rings, ancient coral, and bubbles trapped in ice cores, scientists are also able to conclude that the world has not been as warm as it is now for more than a thousand years. In fact, the Earth has probably never warmed as fast as it has done in the past 30 years. Eleven of the last 12 years (1995 to 2006) rank among the dozen warmest since 1850, the first year for which instrument-based records of global surface temperatures exist.

Meanwhile, it has been shown that global greenhouse gas emissions grew by 70 percent between 1970 and 2004. If current trends continue, atmospheric CO2 concentrations will reach levels sufficient to raise global temperatures by around 2°C to 5°C by the end of this century. Some warming is certain, but the exact scale of temperature increases will be determined by positive feedbacks involving the oceans, clouds, melting ice, and changes to vegetation.

If it weren't for the forests and oceans that absorb around half of the CO2 we produce, global warming would be even more pronounced. However, recent research suggests that nature's ability to absorb the gas could now be stretched to the limit and that natural CO2 "sinks," such as forests and peat bogs, are actually starting to release CO2.

What happens when the world heats up?
A degree or two of warming may not sound like much, but even a small amount of global warming creates many predictable and unpredictable changes. Mountain glaciers and snow cover have already declined in both hemispheres. Arctic sea ice is melting faster every year. Melting glaciers and precipitation are causing some lakes and rivers to overflow, while evaporation is emptying others. Global average sea level rose at an average rate of 1.8 mm per year from 1961 to 2003. The rate was faster from 1993 to 2003: about 3.1 mm (0.12 inches) per year. And the poleward migration of a whole range of animals and plants is almost certainly due to global warming.

Research by the United Nations Intergovernmental Panel on Climate Change (IPCC)-the most authoritative source of scientific research on global warming-suggests strongly that the world is already changing in line with forecasts from computer models that include greenhouse gases as an integral factor. Early global warming models tried simply to anticipate levels of CO2 and other greenhouse gases in the atmosphere. But the latest models can now incorporate some of the ecological feedback mechanisms that, in some cases, act to cool the planet, while others exacerbate the warming-in short, climate change.

"Whereas five years ago we were seeing evidence of climate change in only parts of the world, regional effects, now we're seeing global effects on plants, animals, and hydrology of the Earth's surface," says Professor Martin Parry of the Met Office, the U.K. government's weather forecasting agency. Parry chaired an IPCC-convened group of 441 scientists who, over the last five years, reviewed 29,000 data sets that focused on such phenomena as early flowering seasons, changes in agricultural productivity, changes in insect migrations, and the intensity of heat waves and storms. Their findings, reported earlier this year, found that in 90 percent of cases, changes occurring worldwide are due to climate change.

No one can say with certainty that global warming is the cause of any single hurricane, heat wave, flood, or drought. But taken together, the increase in the frequency and intensity of such events during the last 10 to 15 years provides strong evidence that climate change is already occurring.

Similarly, no one can say with certainty what will happen if global warming continues unchecked. But it's likely that it could lead to a greater occurrence of droughts and heat waves and a greater incidence of extreme weather, including potently destructive hurricanes and tornadoes. The disruption of natural ecosystems such as coral reefs could leave many species struggling to migrate quickly to areas in which they might survive. Sea levels would rise as the oceans expand. Some estimate that a rise in sea level of6 meters-or nearly 20 feet-is possible, enough to flood land occupied by billions of people. Diseases such as malaria and dengue fever would spread faster. Some crops would thrive, while others would be decimated.

It hardly needs saying that people in the poorest parts of the world, such as Africa, will be the least equipped to deal with the effects of global warming.

In a report published in April, the IPCC concluded that a 1°C warming would decrease agricultural yields in the low latitudes; a 2°C rise from today's temperatures would cause the extinction of 30 percent of species; between 2°C and 3°C of warming would increase agricultural yields in the high latitudes, but yields would then decrease with higher global temperatures; and a 3°C warming would lead to widespread coral deaths.

What's to blame?
Very few scientists still need convincing that the warming is anthropogenic-in other words, that people are causing climate change by burning nature's vast stores of fossil fuels: coal, oil, and natural gas. This releases billions of tons of CO2 every year.

A handful of skeptics think we are witnessing natural, not man-made climate change-that the Earth sometimes cools, sometimes warms for reasons that we do not yet fully understand. Yet it is clear that since the start of the Industrial Revolution, we have superimposed onto these natural forces around 1,000 billion tons of greenhouse gases that have amplified the effect.

Another loose affiliation of scientists and writers is promoting the idea that global warming has more to do with fluctuations in solar activity. It's true that 40 percent of the Earth's warming is due to solar activity. But since 1980, sunspot activity has been declining while temperatures here on Earth have been soaring to the highest levels ever recorded.

The IPCC has also found that natural forces are unlikely to be the sole cause of global warming. The results of models that include only natural influences on temperature, such as volcanoes and solar activity, are significantly less accurate than models that also include greenhouse gases.

Can we believe the IPCC?
Established by the U.N. in 1988, the IPCC produces reports every five to six years-reports that are produced by scientists with acknowledged expertise who have to convince thousands of their peers that their opinions are backed by rigorous evidence. For months, scientists contributing to the IPCC lock horns over the evidence until they reach consensus. Their conclusions are then discussed and finalized by representatives of 190 national governments. This means that the panel's reports are conservative. But it also means that they are as trustworthy as a scientific document can be.

What can be done?
We will need to cut CO2 emissions by 70 to 80 percent just to stabilize atmospheric CO2 concentrations and halt global warming. Under the terms of the 1997 Kyoto Protocol, which finally came into force during 2005, many industrialized countries committed to reducing their greenhouse gas emissions by modest amounts. The next round of U.N. policy talks aimed at securing a successor to the Kyoto Protocol will take place in November 2007, in Indonesia.

In the medium to long term, we must also quickly improve the efficiency of our energy use and develop renewable non-carbon fuels like wind, solar, tidal, wave, and perhaps nuclear power.

However, in the short term, scientists say governments must put in place measures to adapt society to the immediate and unavoidable consequences of climate change: adaptations such as building dikes to protect coastal developments from sea-level rises and sowing genetically modified crops that can grow with less water.

"We can make near-term adaptations that will buy us time before emissions controls begin to bite," says Parry. "Even if governments can agree on substantial reductions of emissions, it will take decades for these to take effect."

In the short term, we can also make changes to our own lifestyles and consumption patterns, conserving resources and contributing to the development of a low-carbon economy that is both equitable and sustainable.

It's not the doomsday scenario that some would have us believe. The human race has been through seven major climatic changes, including ice ages, in the last million years. Admittedly, it took thousands of years to adjust, whereas this current climate change will involve an adjustment in little more than two centuries. But scientists are convinced it can be done.

Why has the United States dragged its feet?
Just recently, the countries of the European Union agreed that by 2020 they will have slashed greenhouse gas emissions to 20 percent below 1990 levels, derived 20 percent of their energy from renewable sources, and switched at least 10 percent of the fuels used in transport to biofuels.

Meanwhile, other countries-including the United States under the Bush administration-have claimed that the scientific uncertainty over the pace of climate change is grounds for delaying action, a tone the president set in his first months in office after he rejected the Kyoto agreement.

The Bush administration has never denied that global warming is happening or that humans play a role in it. But speaking in 2001, the president said: "We do not know how much our climate could, or will, change in the future. We do not know how fast change will occur, or even how some of our actions could impact it."

The United States is the biggest emitter of greenhouse gases-responsible for 30 percent of all the human-produced greenhouse gas emissions to date-followed by China. But while China has ratified the Kyoto Protocol, it and other developing countries like India are not bound by it to limit their greenhouse gas emissions. Their commitments are simply to deliver accounts of their emissions to the U.N. The United States and other developed nations like Australia have repeatedly cited these unregulated emissions when explaining why they refuse to ratify the Kyoto Protocol.

"In the United States, there was for a long time a strong effort by fossil-fuel and other corporations, spending millions of dollars and with well-organized lobbying and media propaganda, to make people doubt the science," says Spencer Weart, director of the Center for History of Physics in Maryland and author of The Discovery of Global Warming. "However, the backwardness of the federal administration is not indicative of the U.S. as a whole. If you consider what is being done by the city and state governments, and also by agencies of the federal government acting on their own, you will find that the U.S. is taking as much action to restrict greenhouse emissions as France or Germany."

And now, finally, it seems the mood within the White House is changing. The president acknowledged "the serious challenge of global climate change" in his State of the Union address, and legislators and officials from 13 countries-including China and India-met on Capitol Hill earlier this year to agree on a plan for combating global warming once the Kyoto Protocol expires. At least six current or expected bills in the Senate will address global warming in some form this year.

However, deep-seated political factors may yet hold back progress-chiefly, the fear that the U.S. economy will suffer if it is subjected to energy restrictions while China and India enjoy unbridled growth.

The latest IPCC report, published in May, estimates that the cost for stabilizing greenhouse gases in the atmosphere will be between 0.2 percent and 3.0 percent of global GDP by 2030. That compares favorably with global economic growth that has averaged almost 3 percent per annum since 2000. Yet the White House Council on Environmental Quality maintains that a 3.0 percent reduction in GDP would result in a global recession. Its chairman, James Connaughton, is on record as saying, "No world leader will pursue a strategy that would lead to economic recession. Our goal is reducing emissions and growing the economy."

Left unchallenged, though, climate change might eventually cost the global economy between 5 and 20 percent of GDP every year, according to a British government report last year.

Can it be done?
The ongoing repair of the ozone layer suggests that global warming can be tackled. The 1987 Montreal Protocol, which restricted the use of CFCs and other ozone-depleting halocarbons, will, according to the Netherlands Environmental Assessment Agency, have prevented the equivalent of between 9.7 and 12.5 gigatons of CO2 from being pumped into the atmosphere every year

"The ozone layer was a simpler problem to fix," says Steve Howard, CEO of the Climate Group and a member of the World Economic Forum's Carbon Standards Disclosure Board. "However, we know that we can address climate change with a modest impact on overall economic growth, with significant benefits and using largely existing technologies.

"It's a question of belief, prioritization, and implementation. Just think of our ability to assimilate change and drive innovation-from the way information technology has changed the world, to the way a railroad was built across the United States in five years without the use of tractors. Failure is not an option."

Related Resources

Related Articles Best Buy Buys into Environmentalism Potable Water: Our Global Drinking Problem Peak Oil: A Slippery Slope See All Related Articles

Related Eco Categories Top 10s Transportation & Travel Science & Technology How to Guides

Topics Health People Food Alternative Energy Recycling

Tip of the Day Let the Sunshine In Know What's Watt See All Tips

Glossary High-efficiency particulate air (HEPA) filter Radiant heat Pressure-treated wood Latex Brownfield Full Glossary

Site Resources Directory Answers Quizzes