The Facts About Global Warming
Global warming is real.
The world is warming – and fast.
Global average temperatures have increased over the past 100 years by about 0.74 degrees Celsius (1.33 degrees Fahrenheit). 11 of the 12 warmest years since we began keeping records (150 years ago) have occurred in the past 12 years. The current global climate 1 is warmer than it has ever been during at least the past 500 years, and probably warmer than it has been for more than a thousand years.
The rate at which temperatures are rising is unprecedented. For comparison, the largest temperature increases in the past million years are those that occurred at the ends of ice ages. The warming that occurred then was part of a gradual process that took about 5,000 years. In contrast, the increase in global average temperature we’re seeing today is abrupt, taking place over decades and in peoples’ lifetimes.
The global warming we’re seeing now is the result of our pollution of the atmosphere by massive amounts of greenhouse gases, primarily from the burning of fossil fuels.
The energy from the Sun drives the Earth’s climate. Incoming solar radiation is absorbed by the surface of the Earth, warming the planet. This energy is then emitted from the Earth’s surface as thermal radiation. Greenhouse gases (largely carbon dioxide) and clouds absorb some of this outgoing radiation, which would otherwise escape to space, and send it back to the Earth’s surface. This is the “greenhouse effect.”
When it’s working properly as part of a balanced system, the greenhouse effect is a good thing, keeping Earth’s temperatures warm enough for life. When things become unbalanced, however, and greenhouse gas concentrations begin to rise, the Earth begins to warm.
Natural exchanges of carbon dioxide were in balance for many thousands of years – with living creatures, growing plants and natural events releasing carbon dioxide, and carbon “sinks” such as the oceans absorbing carbon dioxide – leading to a relatively steady concentration of carbon dioxide in the atmosphere. The concentration of carbon dioxide in the atmosphere is now known accurately for the past 650,000 years. During this period, the concentration of carbon dioxide in the atmosphere varied between a low of about 180 parts per million (ppm) during ice ages, and a high of about 300 ppm during warm periods. In the past, before human industrialization, the so-called “carbon budget” was balanced.
Human-caused emissions of greenhouse gases, primarily from the burning of fossil fuels, have busted the carbon budget. Since the beginning of the industrial era, atmospheric concentrations of carbon dioxide have climbed to their highest point in the last half-million years, rising from a bit under 300 ppm in 1900 to over 380 ppm today, and rising at about 2 ppm per year. The increases in global average temperature we’re seeing today are the result of human-caused increases in atmospheric greenhouse gases, which have heightened the greenhouse effect well beyond its natural level. We’re moving off the charts, performing a one-shot, uncontrolled experiment with the only Earth we have.
We are beginning to see the impacts of climate change today.
Global average temperatures are increasing. This doesn’t mean that temperatures are increasing at every location on the planet, or that no place has seen a cold winter in recent years (in fact, a few areas have cooled since the turn of the century). What it does mean is that, on average, when we look at the data, it’s clear that we’re now living in a warming world. Some of the first signs of things to come are set forth below.
We are experiencing more of the warming in winter, which reduces snow pack, ice, and the length of river seasons. Changes in winter temperatures cause more precipitation to fall as rain rather than snow, which results in less water available when it’s needed. These changes are of particular concern to states like California, which rely heavily on irrigation and sophisticated water delivery systems. See Global Warming's Impacts in California.
Since the 1950s, in North America and other locations, there has been a decrease in very cold days and nights and an increase in the number of extremely hot days and warm nights. These changes affect crops, which can cause food shortages and higher prices. And they cause human health impacts in the summer as heat waves become longer and more extreme. Global warming may already have increased the risk of serious heatwaves such as the one that struck Europe in 2003 and caused some 35,000 excess deaths.
Because of rising temperatures during the last century, there has been a dramatic reduction of ice and snow-covered areas, and of frozen subsoil, called permafrost. These changes are affecting people who live in the colder parts of the world. Newtok, a small coastal village in Western Alaska, is just one of them. Like many Native Alaskan villages, Newtok was founded long ago on permafrost. The permafrost on which Newtok rests is now melting, and the sea ice that would normally protect it from fall storms is gone. In the face of sinking buildings and an eroding coast, Newtok’s 315 residents are now seeking to move the town. The move could cost at much as $130 million.
Glaciers are disappearing in many places throughout the world. For example, in 2002, 1,250 square miles of the Antarctic Larsen B ice shelf suddenly collapsed. Glacier National Park in Montana has a mere 26 named glaciers today, down from 150 in 1850, and these remaining glacier are much reduced. Scientists predict that there may be no glaciers in the Park by 2030.
Melting land ice and thermal expansion of the oceans is causing rising sea levels, eroding beaches and threatening to displace people who live in low-lying areas and on islands. For the Pacific nation of Tuvalu, global warming has arrived. Over the past few years, seasonal “king tides” have risen higher than ever, washing over the island’s main roads and destroying crops and property. If trends continue, in the coming decades, the island’s 11,800 people must find another home. Many Pacific islands, including Kiribati, Tokelau, and the Marshall Isles, are similarly vulnerable. See Global Warming's Unequal Impacts.
And we are seeing more extreme weather. While no individual weather event can be attributed to global warming, increases in the destructive potential of hurricanes are strongly correlated with increases in tropical sea surface temperatures. Since 1970, the number of category 4 and 5 hurricanes increased by about 75%. This suggests that events like Hurricane Katrina, which devastated the Gulf Coast in 2005, may become the norm and not the exception.
If we don’t drastically reduce our greenhouse gas emissions, the climate impacts we are only beginning to see are likely going to get worse, and, as some point, we may even lose the ability to control the problem.
The experts tell us that an additional increase in global average temperatures of just 2 degrees Celsius (3.6 degrees Fahrenheit) is very likely dangerous 2. Even if we stopped burning fossil fuels today, we’re already committed to a good portion of this temperature increase – about 0.6 degrees Celsius (a bit over 1 degree Fahrenheit) by the end of the century – because of the carbon we’ve dumped into the system.
With a 3.6 degree Fahrenheit increase, we can expect to see disastrous effects, including increased frequency of droughts and floods, more extreme and more frequent severe weather, more wildfires, increasingly rapid sea level rise, and increased stress on wildlife and plants. The environmental effects will undoubtedly lead to serious economic, political, and national security disruptions, as the residents of entire regions are displaced from their homes or are unable to obtain food and water in the areas they live.3
At temperatures above this range, we also risk setting in motion unstoppable “feedback loops” that will exacerbate global warming. For example, the disintegration of large areas of snow and ice will expose darker surfaces that absorb more sunlight, raising temperatures and speeding up the further loss of snow and ice. Higher temperatures will thaw the arctic tundra, causing organic materials in the permafrost to decompose, thereby releasing large amounts of methane. Methane is a powerful greenhouse gas – 21 times more potent than carbon dioxide. Similarly, higher temperatures and droughts will lead to increased and larger wildfires. The wildfires will, in turn, release stored carbon to the atmosphere, heightening the global warming effect. And warmer oceans will be less able to absorb carbon dioxide, leaving more carbon dioxide in the atmosphere. These feedback loops may already have begun.
To have any chance of staying below a dangerous increase in temperature, we must stabilize atmospheric concentrations of carbon dioxide at not more than about 450 ppm. On our current path, atmospheric concentrations of carbon dioxide will likely exceed 700 ppm by the end of the century.
And we must act today. According to Rajendra Pachauri, a scientist and economist who heads the Intergovernmental Panel on Climate Change, “If there’’s no action before 2012, that’s too late. What we do in the next two to three years will determine our future. This is the defining moment.”4
If we fail to take prompt, decisive action to change from “business as usual,” the coming generations will likely find a way to survive. But the world we leave them will be a profoundly different world than the one we enjoy.
For more information, please visit:
The Intergovernmental Panel on Climate Change (IPCC), Fourth Assessment Report, Working Group I: The Physical Science Basis of Climate Change, Frequently Asked Questions at http://ipcc-wg1.ucar.edu/wg1/Report/AR4WG1_Print_FAQs.pdf
California Air Resources Board, Backgrounder / The Greenhouse Effect and California at http://www.arb.ca.gov/cc/factsheets/ccbackground.pdf
NASA, Goddard Space Flight Center, Global Warming and Climate Change Policy Websites (list of links) at http://globalchange.nasa.gov/Resources/pointers/glob_warm.html
- “Climate” is average temperature, precipitation and wind in a given region over an extended period of time. It’s sometimes called “average weather.”
- Temperature increases are measured against global average temperatures from 1980-1999.
- See IPCC, Fourth Assessement Report, Working Group II: Impacts, Adaption and Vulnerability, Summary for Policymakers at http://www.ipcc.ch/pdf/assessment-report/ar4/wg2/ar4-wg2-spm.pdf#page=10.
- Elisabeth Rosenthal, U.N. Chief Seeks More Climate Leadership, N.Y. Times, Nov. 18, 2007, available at http://www.nytimes.com/2007/11/18/science/earth/
18climatenew.html?n=Top/News/Science/Topics/Air%20Pollution.