Science

The Science Behind the Shrinking Arctic Ice Cap

September 2007

The Arctic ice cap declined to a record minimum size in summer 2007. Studies indicate this accelerated shrinkage of Arctic sea ice may be in response to a strong warming trend and that the climate reacts more strongly to a given amount of global warming than generally believed.

The Arctic ice cap consists of a continent-sized sheet of sea ice that floats at the surface of the Arctic Ocean. During the dark of winter, the ice cap covers nearly the entire Arctic Ocean, but during the summer constant sunlight melts the edges of the ice cap, causing it to shrink in area. This annual shrinking begins in early spring and progresses into mid-September, when the extent of the ice cap reaches its summertime minimum and begins to grow again as the sun sets for the year and the chill of winter returns. Since 1979, the extent of the Arctic sea ice has been monitored using satellite observations. During this time, the September minimum extent has declined on average as the Arctic has warmed. Since 2000, there has been a series of record-breaking low annual minima, with 2002, 2005, and 2007 each establishing new records. View Graph

On August 17, 2007, the National Sea Ice Data Center (NSIDC) reported: “Arctic sea ice surpassed the previous single-day (absolute minimum) record for the lowest extent ever measured by satellite.” One month later, the NSIDC reported that the ice cap had reached it annual minimum size (Figure 1), which was “4.13 million square kilometers (1.59 million square miles), compared to 5.32 million square kilometers (2.05 million square miles) in 2005.” Compared to the long-term average between 1979 and 2000, The 2007 minimum “was lower by 2.61 million square kilometers (one million square miles), an area approximately equal to the size of Alaska and Texas combined, or the size of ten United Kingdoms.” (NSIDC, 2007b).

The wintertime maximum area of the ice cap occurs in March and has also been shrinking. The annual maximum sea ice extent reached record-breaking lows in three consecutive winters (2004-2006). In March 2007, the maximum extent was the second lowest on record after 2006. Regarding this observation, NSIDC scientist Walt Meier said, “This year's low wintertime extent is another milestone in a strong downward trend. We're still seeing near-record lows and higher-than-normal temperatures. We expect the downward trend to continue in future years” (NSIDC, 2007a).

In recent months, some important peer-reviewed studies have been published on the observed and projected shrinkage of the Arctic ice cap. In April, scientists from NSIDC and the National Center for Atmospheric Research published a study documenting from long-term observations that climate models underestimate the rate of Arctic sea ice loss (Stroeve et al., 2007). Observed loss of sea ice from 1953 to 2006 occurred three times faster than the average rate projected for the same period by 18 of the latest generation of climate models used by the Intergovernmental Panel on Climate Change (IPCC). According to a recent review of the scientific evidence, the observed ice loss “is best viewed as a combination of strong natural variability… and a growing radiative forcing associated with rising concentrations of atmospheric greenhouse gases…” (Serreze et al., 2007).

This summer, the initial rate of Arctic sea ice decline was similar to previous record-breaking years, but in late June and early July there was a dramatic surge in the rate of loss that led to the early arrival of the record-low sea ice extent reached in August (Figure 2). Regarding this surge, the NSIDC said, “…sea ice declined at a pace of up to 210,000 square kilometers (81,081 square miles) per day, or the equivalent of an area the size of Kansas each day. This rate was unprecedented in the satellite record…” (NSIDC, 2007b). View Graph

The cause of this surge is unclear, but is consistent with recent modeling research suggesting that sudden, extreme acceleration of shrinkage may be an inherent response of Arctic sea ice to a strong warming trend (Holland et al., 2006). In this study, about half of the model projections exhibited sudden accelerations in sea ice loss. In the model projections where such events occurred, trends in ice loss were four times faster than in projections without abrupt accelerations. If such accelerations are inherent to the response of sea ice to persistent warming, the Arctic could be ice free during the summer well before the end of this century (Serreze et al., 2007), a condition that has not existed for at least one million years and probably much longer (Overpeck et al., 2005).

The loss of Arctic sea ice is not the only aspect of climate change that has been underestimated by projections. Recent observations indicate that climate models have underestimated ice loss from the Greenland and Antarctic ice sheets (Shepherd & Wingham, 2007), ice loss from mountain glaciers (Meier et al., 2007), the rate of global sea level rise (Rahmstorf et al., 2007), change in global precipitation (Wentz et al., 2007; Zhang et al., 2007), and response of northern forests to warming (Soja et al., 2007). All of these changes were predicted before they were detected, but they are occurring sooner or more rapidly than expected (Engelhaupt, 2007). Although there are probably multiple reasons for underestimating climate change and ecosystem responses to it, inadequately treated positive feedbacks (amplifying factors within the climate system itself) are probably involved (Pittock, 2006).

The unexpectedly rapid change in Arctic sea ice and other climate processes suggests that the climate reacts more strongly to a given amount of global warming than scientists have calculated. As a result, risks from future climate change are likely greater than scientists have generally believed, and existing climate change projections might best be viewed as the minimum changes that humanity should expect.

References

Engelhaupt, E. 2007. Models underestimate global warming impacts.

Environmental Science & Technology, 41, 4488-4489.

Holland, M. M., Bitz, C. M. & Tremblay, B. 2006. Future abrupt reductions in the summer Arctic sea ice. Geophysical Research Letters, 33, L23503, doi:10.1029/2006GL028024.

Meier, M. F., Dyurgerov, M. B., Rick, U. K., O’Neel, S., Pfeffer, T., Anderson, R. S., Anderson, S. P. & Glazovsky, A. F. 2007. Glaciers Dominate Eustatic Sea-Level Rise in the 21st Century. Science, 317, 1064-1067.

NSIDC. 2007a. Arctic Sea Ice Narrowly Misses Wintertime Record Low. National Sea Ice Data Center. Available online: http://nsidc.org/news/press/ 20070403_winterrecovery.html

NSIDC. 2007b. Arctic Sea Ice News Fall 2007. National Sea Ice Data Center. Available online: http://nsidc.org/news/press/2007_seaiceminimum/20070810_index.html.

Overpeck, J. T., Sturm, M., Francis, J. A., Perovich, D. K., Serreze, M. C., Benner, R., Carmack, E. C., III, F. S. C., Gerlach, S. C., Hamilton, L. C., Hinzman, L. D., Holland, M., Huntington, H. P., Key, J. R., Lloyd, A. H., MacDonald, G. M., McFadden, J., Noone, D., Prowse, T. D., Schlosser, P. & Vörösmarty, C. 2005. Arctic System on Trajectory to New, Seasonally Ice-Free State. Eos, 86, 309-316.

Pittock, B. A. 2006. Are Scientists Underestimating Climate Change? Eos: Transactions of the American Geophysical Union, 34, 340-341.

Rahmstorf, S., Cazenave, A., Church, J. A., Hansen, J. E., Keeling, R. F., Parker, D. E. & Somerville, R. C. J. 2007. Recent climate observations compared to projections. Science, 316, 709 (doi:10.1126/science.1136843).

Serreze, M. C., Holland, M. M. & Stroeve, J. 2007. Perspectives on the Arctic’s shrinking sea-ice cover. Science, 315, 1533-1536.

Shepherd, A. & Wingham, D. 2007. Recent sea-level contributions of the Antarctic and Greenland ice sheets. Science, 315, 1529-1532.

Soja, A. J., Tchebakova, N. M., French, N. H. F., Flannigan, M. D., Shugart, H. H., Stocks, B. J., Sukhinin, A. I., Parfenova, E. I., III, F. S. C. & Jr., P. W. S. 2007. Climate-induced boreal forest change: Predictions versus current observations. Global and Planetary Change, 56, 274-296.

Stroeve, J., Holland, M. M., Meier, W., Scambos, T. & Serreze, M. 2007. Arctic sea ice decline: Faster than forecast. Geophysical Research Letters, 34, L09501, doi: 10.1029/2007GL029703.

Wentz, F. J., Ricciardulli, L., Hilburn, K. & Mears, C. 2007. How Much More Rain Will Global Warming Bring? Science, doi:10.1126/science.1140746.

Zhang, X., Zwiers, F. W., Hegerl, G. C., Lambert, F. H., Gillett, N. P., Solomon, S., Stott, P. A. & Nozawa, T. 2007. Detection of human influence on twentieth-century precipitation trends. Nature, 448, 461-465.

IPCC Fourth Assessment Report, Working Group III

IPCC AR4 WGIII: "Mitigation of Climate Change"

Climate Change Basics Fact Sheets

Coal facts on our Energy & Technology page
Sea Level Rise - The State of the Science
The Causes of Global Climate Change (pdf)
Hurricanes - Are They More Frequent?
The Arctic - Is It Warming Faster Than The Rest Of The World?
Climate Impacts in the Arctic and Antarctic
NASA Temperature Correction

Kids Corner

Welcome Kids!

Penguins To help more kids better understand global warming, we collaborated with Nickelodeon to research children's and parents' attitudes and behaviors toward the environment.

There's a lot you can learn about global warming. To help, this page provides answers to six key questions about global warming, how it occurs, and how you can help to stop the process. For more tips on actions people can take, visit our What You Can Do page.

You can also explore other kid-oriented sites from the list on this page.

Key Questions

Do scientists agree about global warming?

Scientists who study the climate are still arguing about how fast the earth is warming and how much it will warm, but they do agree that the earth is warming and that it will keep warming if we don’t do anything about it.

What is causing global warming?

Scientists agree that the burning of fossil fuels like oil and coal cause greenhouse gases to escape into the air and that these gases are causing most of the warming. Another cause is deforestation (cutting down trees). Trees soak up carbon dioxide, one of the greenhouse gases, from the air.

What is the difference between "global warming" and "climate change?"

"Global warming" refers to the increase of the Earth's average surface temperature, due to a build-up of greenhouse gases in the atmosphere. "Climate change" is a broader term that refers to long-term changes in climate, including average temperature and precipitation.

What will happen if global warming continues?

There are already some changes happening because of global warming. Sea level is rising and some animals are already moving to new homes. It’s already too late to stop global warming completely.

If the warming gets worse, as scientists expect, there may be some kinds of plants and animals that become extinct (disappear completely) because they can’t move to new homes. There may be more storms and floods. Sea level may rise so much that people have to move away from the coasts. Some areas may become too dry for farming.

What is being done about global warming?

Global warming is a very difficult problem to fix. People are having a hard time agreeing on what to do about it. For example, everyone agrees that wasting energy is a bad thing to do. But some people think that the federal government should make laws about it, while other people think it should be up to each person or business to decide what to do.

Many states and businesses in the United States are not waiting until the federal government decides what to do. They have already started working on the problem.

What can I do about global warming?

You don’t have to wait until you are grown to do something about global warming. Scientists agree that the burning of fossil fuels is causing global warming. Since these fuels are burned for energy, and everyone uses energy, everyone can help stop global warming just by using less energy.

Think about the things you do each day that use energy. The lights in your house use electricity. The TV and computer use electricity. The washing machine, dishwasher and dryer all use gas or electricity. Every time you ride in your car, it uses gasoline.

There are some simple things that you can do to help stop global warming:

Wait until you have a lot of clothes to wash before using the washing machine. Don’t use the machine for one item just because it’s your favorite shirt.

Turn off the lights when you leave a room. Use fluorescent bulbs in your room.

Turn off your computer or the TV when you’re not using it. Unplug chargers when not in use.

Close the blinds on a hot day if the sun is shining in. Dress lightly instead of turning up the air conditioning. Or use a fan.

Dress warmly inside your house when it’s cold, instead of turning up the heat.

Bike or walk short distances instead of asking for a ride in a car.

Plant a tree.

Take shorter showers. Heating water uses energy.

Learn more about global warming so you can talk to people about it. See: Could it really happen?

For more tips, click here.

Basic global warming information facts for kids to learn how to stop the process.

IPCC Fourth Assessment Report: Climate Change 2007

The Intergovernmental Panel on Climate Change (IPCC) was established by the World Meteorological Organization (WMO) and the United Nations Environment Programme (UNEP) to assess scientific, technical and socio-economic information relevant for the understanding of climate change, its potential impacts and options for adaptation and mitigation. The Fourth Assessment report was released in three installments over the course of 2007, with the final synthesis report published in November 2007. Details on the most current release, including a Pew summary and statement, can be found below.

IPCC Summary For Policymakers to the Fourth Assessment Report

To view each working group's report, as well as our statements and related content, click on the working group's title below

Summary for Policymakers, Release Date: November 17, 2007
Working Group III - "Mitigation of Climate Change", Release Date: May 4, 2007
Working Group II - "Impacts, Adaptation & Vulnerability", Release Date: April 6, 2007
Working Group I - "The Physical Science Basis", Release Date: February 2, 2007

To view published installments in their entirety, visit the IPCC website.

Scientists from all over the world contributed to the findings discussed in the Fourth Assessment Report. For more information on the work of some of these scientists, visit: National Center for Atmospheric Research.

About the IPCC

In 1988, recognizing the problem of global warming, two UN agencies, the World Meteorological Organization and the United Nations Environment Programme, established the Intergovernmental Panel on Climate Change (IPCC). The IPCC does not conduct independent research, rather it convenes climate experts from around the world every five to seven years in order to synthesize the latest climate research findings in peer reviewed and published scientific/technical literature. Visit the IPCC website: www.ipcc.ch.

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About the Fourth Assessment Report

The IPCC issued comprehensive assessments in 1990, 1996, and 2001; its Fourth Assessment Report (AR4) will be released in installments during 2007. The AR4 is the most comprehensive synthesis of climate change science to date. Experts from more than 130 countries are contributing to this assessment, which represents six years of work. More than 450 lead authors have received input from more than 800 contributing authors, and an additional 2,500 experts reviewed the draft documents.

AR4 will comprise three sections, or working groups, that deal with the scientific basis of global warming (Working Group I), its consequences (Working Group II), and options for slowing the trend (Working Group III). The IPCC will release summaries of the three working group documents over the course of 2007, culminating in the publication of the final “synthesis report” at the end of the year.

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IPCC Fourth Assessment Report, Working Group II

IPCC AR4 WGII: "Impacts, Adaptation & Vulnerability"

IPCC Fourth Assessment Report, Working Group I

IPCC AR4 WGI: "The Physical Science of Climate Change"

Statement: IPCC Fourth Assessment Report, Working Group II

Intergovernmental Panel on Climate Change (IPCC) Releases New Assessment Report on the Impacts of Climate Change

Statement by the Pew Center on Global Climate Change

April 6, 2007

The IPCC Fourth Assessment “Summary for Policymakers” Working Group II report represents the IPCC’s strongest statement to date on the impacts of global climate change. Because of a dramatic increase in the number and quality of observations, this report concludes that, “it is likely [better than 2:1 odds] that anthropogenic warming has had a discernible influence on many physical and biological systems.” The report also projects with greater confidence than in the past that many regions, including North America, will experience severe impacts in the future, even for moderate warming scenarios. Particularly vulnerable are low-lying coastal regions worldwide. Many poor countries at low latitudes are also particularly vulnerable because of a combination of strong climate impacts, low capacity for adaptation, and heavy reliance on climate-impacted resources, such as local food and water supplies.

The assessment is based on extensive published, peer-reviewed scientific literature. Today’s report is the second of three major studies that comprise the Fourth Assessment with input from more than 1,200 authors and 2,500 scientific expert reviewers from more than 130 countries. The first report, released in February 2007, examined the physical science basis for climate change. The third report, to be released in May 2007, will explore the solutions to global climate change, particularly options for reducing greenhouse gas emissions.

Statement by Eileen Claussen, President Pew Center on Global Climate Change

April 6, 2007

This week began with a landmark decision by the US Supreme Court and ended with the release of the IPCC's 4th Assessment on climate change impacts. Following the Supreme Court's decision, it's clear that EPA has the authority – and should -- regulate CO2, and the IPCC report delivered the strongest statement to date on the consequences of climate change. Taken together with increasing calls from CEOs, states, and the public, the message is loud and clear: Read our lips - We need mandatory climate policy in the United States.

Trends in CO2 Emissions

This figure shows emissions of carbon dioxide (CO₂) by fuel source across all sectors of the economy. The fuels shown are coal, natural gas, petroleum, as well as the total emissions.

Overall, coal and petroleum consumption are down since 2007, while natural gas use has increased. In the electric power sector, natural gas, which emits about half the amount of CO₂ as coal, is being used more extensively due to its lower price. In the transportation sector, petroleum consumption is down due to an increase in car and light truck fuel economy (for a similar number of vehicle miles traveled, year-on-year). Correspondingly, total emissions have declined since 2007.

Source: EIA (2012)

U.S. CO2 Emissions from the Electric Power Sector

This figure shows the emissions of carbon dioxide (CO₂) from the burning of fossil fuels for electric power generation. The electricity-generating fuels shown here are coal, natural gas, petroleum and non-biomass waste. Natural gas, which emits about half the amount of CO₂ as coal, is being used more extensively due to its lower price and displacing coal-fired generation, while petroleum-fired electricity generation continues to be retired.

Source: EIA (2012)

Science

The Science Behind the Shrinking Arctic Ice Cap

IPCC Fourth Assessment Report, Working Group III

IPCC AR4 WGIII: "Mitigation of Climate Change"

Related Content

Climate Change Basics Fact Sheets

Kids Corner

IPCC Fourth Assessment Report: Climate Change 2007

IPCC Fourth Assessment Report, Working Group II

IPCC AR4 WGII: "Impacts, Adaptation & Vulnerability"

Related Content

IPCC Fourth Assessment Report, Working Group I

IPCC AR4 WGI: "The Physical Science of Climate Change"

Related Content

Statement: IPCC Fourth Assessment Report, Working Group II

Trends in CO2 Emissions

U.S. CO2 Emissions from the Electric Power Sector