Understanding Climate Change

Topics

The Intergovernmental Panel on Climate Change and NCAR

Frequently Asked Questions

• FAQs: Global Warming and Climate Change
• The Physical Science of Climate Change: What's in the Working Group I Summary? (opens new window)
• Climate Change Impacts: What's in the Working Group II Summary? (opens new window)

News

• Related research news and features
• NCAR Experts: Working Group I | Working Group II
•  Teleconferences featuring IPCC scientists (April 6 and February 2)

An IPCC 2007 timeline Working Group I: The Physical Science Basis Summary for Policymakers - February 2, 2007, Paris, France Working Group II: Impacts, Adaptation and Vulnerability Summary for Policymakers - April 6, 2007, Brussels, Belgium Working Group III: Mitigation of Climate Change Summary for Policymakers (PDF) - May 4, 2007, Bangkok, Thailand The Synthesis Report Review by governments and experts: May 21 - July 12, 2007 Adoption and approval at the 27th Session of the IPCC: November 12-16, 2007, Valencia, Spain: Synthesis Report Final reports from the three working groups: IPCC Fourth Assessment Report: Climate Change 2007.

Experiments using computer models confirm the importance of human-produced emissions in the temperature trends of recent decades. This graphic depicts global average temperature since 1890 as reproduced by the NCAR/DOE Parallel Climate Model. The blue line summarizes simulations performed using only natural influences on climate (volcanoes and solar variations). The red line, from a set of simulations that includes sulfate aerosol pollution and greenhouse gases, is much closer to the observed record (black line). The blue and red shading shows the range of results (the model uncertainty) for each group of simulations, or ensemble. (Illustration courtesy Gerald Meehl, NCAR. News media terms of use*)

A worldwide effort

About 25 NCAR researchers and a nearly equal number of support staff participate in the assessments of the Intergovernmental Panel on Climate Change, a group that includes more than 2,000 experts from 154 countries. Together, these experts cover a vast array of climate specialties. Their reports take years of thorough scientific investigation and review before they are issued to the public.

The IPCC, sponsored by the United Nations and the World Meteorological Organization (a UN agency), released assessments in 1990, 1996, 2001, and 2007. In late 2007, participants in all the IPCC assessments since 1990 shared in the Nobel Peace Prize.

The IPCC released its Fourth Assessment Report in segments throughout 2007 (see timeline at right). The report draws extensively on studies using the NCAR-based Community Climate System Model (CCSM), along with climate models from other research centers around the world.

In addition to reviews by individual scientists and scientist panels, each chapter is also scrutinized by representatives of the governments participating in the IPCC process. While governments negotiate on how the findings are worded, the final product is based on a scientific, not a political, concensus.

After six years of planning, collecting, writing, and responding to multiple reviews, the Fourth Assessment Report reflects the scientific consensus on what is known and what is still uncertain about the environmental and societal consequences of continuing to add greenhouse gases to Earth's atmosphere.

• Working Group I reviews the physical science, including observations and computer modeling of the past, present, and future
• Working Group II examines the likely impacts on people and the environment.
• Working Group III explores policy options for lessening the likelihood of climate change.

Each working group prepares a lengthy report and a much-briefer "Summary for Policymakers."

• What's in the Working Group I Summary for Policymakers on the Physical Science of Climate Change? (opens new window)
  
  
• What's in the Working Group II Summary for Policymakers on Climate Change Impacts? (opens new window)
  
  

• Working Group III Summary for Policymakers (PDF)

NCAR contributors to the latest IPCC reports and a brief summary of activities are listed in the NCAR 2007 Annual Report.

Learn more about the IPCC and about the assessment reports at the Web site of the Intergovernmental Panel on Climate Change.

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Take a tour of NCAR's research on climate change

Hasn't Earth been much warmer in the past? Is human activity the only explanation for global warming? What about natural cycles like El Niño? For a quick tour of the major issues and updates on NCAR projects, visit NCAR Climate Research, or jump to a page of interest:

Earth's past climates
Our climate has been constantly changing since Earth began—long before human beings and their activities. But modern weather measurements go back only 100 to 150 years. How do we know what Earth and its climate were like in prehistoric times? Some clues come from Earth itself. more >

How do we know Earth is warming now?
For more than 100 years, Earth's surface temperature has been monitored by a global network of land-based weather stations, supplemented by readings taken across the oceans. Together, these data show that Earth's surface air temperature has risen more than 1.1°F (0.7°C) since the late 1800s. Researchers have identified human activities that amplify the greenhouse effect as a major culprit. more >

Climate of the future
Climate simulations at NCAR have shown that changes in the Sun's intensity explain less than a third of the global warm-up during the last century. The most likely explanation for a warming Earth is the greenhouse gases emitted when fossil fuels are burned. The effects of future climate change will be far more varied than a simple and uniform warming over the entire planet, with some regions considerably hotter or cooler, or wetter or drier, than others. more >

El Niño and La Niña
This large-scale oceanic warming affects most of the tropical Pacific. The weather impacts related to El Niño and its cool-ocean counterpart, La Niña, extend throughout the Pacific Rim to eastern Africa and beyond. Together they provide one of the main sources of year-to-year variation in weather and climate around the world. more >

Drought and wildland fire
When reliable rainfall disappears from a region for years or even decades, the impacts on flora, fauna, and people can be profound. Through exhaustive analyses, NCAR scientists have helped pinpoint how large-scale climate cycles can produce drought at far-flung locations. Where drought does strike, the risk of wildland fire soars. NCAR has launched an innovative, multidisciplinary project to address this concern. more >

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Delve deeper with NCAR's climate modelers and analysts

New materials have been added to our Web site by scientists in NCAR's Earth and Sun Systems Lab/Climate and Global Dynamics Division. Visit CGD Climate Highlights, or jump to a page of interest:

Why do we believe the climate is changing?
The globe is warming. Averaged over all land and ocean surfaces, temperatures today are about 0.75ºC warmer than at the beginning of the 20th Century. Rates of temperature rise are greater in recent decades: since 1979, global surface temperatures have increased more than 0.4ºC. Land regions have warmed the most (0.7ºC since 1979), especially over the Northern Hemisphere continents. The warmest year in the 145-year global instrumental record is 1998, since the major 1997–98 El Niño enhanced it. The year 2005 is the second warmest on record, followed by the years 2002–2004. Based on reconstructions of temperature from proxy data, like tree rings and ice cores, several studies have also concluded that Northern Hemisphere surface temperatures are warmer now than at any time in at least the last 1,000 years. more >

Related Topics: Surface Temperature | Extreme Events | Hurricanes and Climate Change | Land & Sea Ice | Attribution

What do we know about past climate variability?
Climate varies naturally on many different time scales. Some variations are regular, such as the heating and cooling from day to night and summer to winter. Other variations are less so. Variations in the tropical Pacific associated with the El Nino–Southern Oscillation phenomenon typically occur every 3 to 5 years. They can lead to droughts in Australia and flooding in the U.S. Gulf Coast states. Climate also varies on much longer time scales from centuries and millennia to tens of thousands of years to million of years. Climate variations on shorter time scales are superimposed on these variations occurring on longer time scales. more >

Related Topics: Arctic warmth | Earth's Deep Past | Sahel rainfall | Past centuries and millenia | Abrupt change

What types of models are used in NCAR's climate research?
The models developed by NCAR's Climate and Global Dynamics Division synthesize fundamental physics, fluid dynamics, chemistry, and descriptions of processes derived from observations and theory. Since the range of climate processes encompassed by these models is so broad, they are developed by truly multidisciplinary teams. more >

Related Topics: CCSM Overview | WACCM Overview | all models

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Zooming in on regional climate change

Most climate change simulations are created with models that simulate the global scale and produce global averages as their results. But to understand how global warming will affect drinking water storage or the ability to grow wheat, corn, and other staples, regional simulations and impact studies are needed.

Regional models depict the climate of a smaller area in more detail, which is challenging because

• scientists are still studying the influence of clouds and local storms and how best to portray them in regional models; global models do not try to represent these fine-scale processes
• many of the other equations created to represent physical processes in global models must have more spatial detail
• the models must reflect changes in the atmosphere, land, oceans, and other parts of the envirronment over shorter time scales
• all of this higher resolution usually requires greater computing power and longer time to run a simulation

	View animations of experimental high-resolution simulations on the new NCAR-based nested regional climate model (NCRM). Each simulation represents one year's evolution, hour by hour, of a key measurement (for example, rainfall, wind), on a scale of 36 kilometers (22 miles). Click here or on the image to open a Web page where the animations can be launched. (©UCAR. News media terms of use*)

NCAR scientists and their colleagues are addressing these issues through development of a nested regional climate model (NRCM). The model's developers plan to

• Seamlessly integrate the weather and climate models based at NCAR to capture all important spatial and temporal scales
• Collaborate with impacts researchers to address both scientific and societal issues
• Provide a new community model freely available to researchers around the world, such as the NCAR-initiated Community Climate System Model (CCSM) and Weather Research and Forecasting Model (WRF).

Scientists hope to improve understanding and simulation of complex, two-way scale interactions, with emphases on:

• downscaling from global climate simulations (especially in investigations of societal impacts)
• upscaling from regional processes, including the effects of land and ocean processes
• the impact of regional weather, particularly the organization of moist convection on larger scales.

Some aspects of regional climate change are already well established. For instance, high-latitude areas such as Canada, Russia, and the Arctic are warming more rapidly than the tropics, as predicted by computer models. This trend is expected to continue. In many nations, rainfall and snowfall are becoming more concentrated in heavier bursts, and regions poleward of latitude 40 degrees north are expected to see more days with heavy precipitation. NCAR scientists and colleagues are working to improve understanding of other potential regional changes in climate, such as where U.S. rainfall and snowfall patterns might shift.

Researchers are also working to improve techniques for assessing the impacts of a changing climate on environment and society. One method is to translate temperature changes from a model into trends that affect people's everyday lives. A 2004 NCAR study found that, by the period 2080-99, American and European heat waves will be more severe, frequent, and long-lasting.

A related study found that frost days (those in which temperatures dip to 0°C or 32°F) will decline in many parts of the globe by 2080-99. The largest decreases are projected across the northwest parts of Europe and North America, as mild marine air becomes more prevalent in winter. Such a change would affect agriculture and tourism as well as natural ecosystems.

Both of these studies, along with many others, have been used in preparing the 2007 IPCC assessment. One theme for the new assessment is the extent to which our planet is committed to some amount of human-induced climate change, regardless of what actions we take in the future.

For a breakdown of already detected and projected regional impacts, including an interactive map, see the section about Impacts on Natural Systems.

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Uncovering North America's climate future

Researchers are developing new approaches to fine-scale computer modeling to allow greater focus on regional impacts of a changing climate. (Image courtesy North American Regional Climate Change Assessment Program, NCAR.)

What will climatic conditions look like for the United States and Canada by the middle of this century? An international team of scientists is focusing in on North American climate from 2040 to 2070, laying the groundwork to create regional simulations with unusually fine detail.

Most projections of future conditions rely on global climate models run on supercomputers that, despite their sophistication, lack the detail to simulate behavior within a state or region. Led by NCAR, the North American Regional Climate Change Assessment Program (NARCCAP) will use an ensemble of global climate models and high-resolution regional climate models to produce simulations with about triple the resolution of most projections of future climate.

The combination of tools will allow scientists to incorporate relatively small topographical features, such as mountain ranges, lakes, and complex coastlines, that can have a significant influence on local and regional climate. An important research benefit of the effort, which is designed to complement similar projects in Europe and South America, will be the ability to compare the results of fine-scale with coarser-scale modeling to more clearly determine the added value of high-resolution projections of future climate.

NCAR scientists are collaborating with colleagues at U.S. universities and laboratories, the University of Quebec and the Ouranos Consortium in Montreal, and Britain’s Hadley Centre for Climate Prediction and Research. The project is expected to spawn additional international collaborations as researchers continue to fine-tune projections of the impacts of climate change on North America.

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Updated: March 2008

*News media reproduction to illustrate this story and nonprofit use permitted with proper attribution as provided above and acceptance of UCAR's terms of use. Find more images in the UCAR Digital Image Library.

The National Center for Atmospheric Research and UCAR Office of Programs are operated by UCAR under the sponsorship of the National Science Foundation and other agencies. Opinions, findings, conclusions, or recommendations expressed in this publication do not necessarily reflect the views of any of UCAR's sponsors.

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