OUR CHANGING PLANET
The U.S. Climate Change Science Program
for Fiscal Years 2004 and 2005

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Climate Variability and Change

Climate variability and change can profoundly influence social and natural environments throughout the world, with consequent impacts on natural resources and industry that can be large and far-reaching. For example, seasonal to interannual climate fluctuations strongly affect agriculture, the abundance of water resources, and the demand for energy, while long-term climate change may alter agricultural productivity, land and marine ecosystems, and the goods and services that these ecosystems supply. Recent advances in climate science are providing information for decisionmakers and resource managers to better anticipate and plan for potential impacts of climate variability and change. Further advances will serve the nation by providing improved knowledge to enable more scientifically informed decisions across a broad array of climate-sensitive sectors.

Research on climate variability and change focuses on two overarching questions:

• How are climate variables that are important to human and natural systems affected by changes in the Earth system resulting from natural processes and human activities?
• How can emerging scientific findings on climate variability and change be further developed and communicated in order to better serve societal needs?

Addressing these questions requires recognition that the problems of climate variability and change cannot be cleanly separated, and that the success of understanding each will require improved understanding of both. For example, future changes in climate variability, for example a variation in the frequency and nature of EN SO events or the severity and duration of droughts, will depend partly on changes in global (and regional) mean conditions. Conversely, climate variations influence global and regional heat and moisture distributions, and hence can substantially alter the global and regional mean response of the climate system to either

natural or anthropogenic forcing. Further, demands for improved climate information span a broad range of timescales, ranging from assessments of current conditions and seasonal forecasts of climate variability that support resource management decisions, to longer-term decadal to centennial-scale projections of climate change that help inform infrastructure planning and policy development.

Current research activities on climate variability and change are directed toward: understanding and, to the extent possible, reducing uncertainties in climate model projections; improving climate predictions on seasonal-to-interannual timescales; improving capabilities to detect, attribute, and project longer-term climate changes; advancing understanding on the causes of past abrupt climate changes and the potential for future rapid changes; determining whether and how climate variations alter the frequencies, intensities, and locations of extreme events; and improving the development and communication of climate information to better the needs of the public and decisionmakers. over the past year, significant advances have been made in several of these areas. Some of the research highlights are summarized below.

Highlights of Recent Research

Highlights of recent research supported by CCSP participating agencies:

Observed Arctic warming trend over the last 20 years:

Observations of Arctic-wide surface temperatures using satellite data have shown that over the period 1981-2001, the Arctic region warmed at an annual average rate of 0.3°C per decade over sea ice (considering those portions of the Arctic Ocean where 80% of ocean surface is covered by ice), 0.5°C per decade over the high latitude (poleward of 60 degrees North) region of Eurasia, and 1.0°C over the high latitude region of North America. Temperature trends derived from surface data are similar over much of the Arctic, but differ in some sub-regions. In comparison, during the last 20 years the global annual average surface temperature has increased by about 0.2°C per decade. At the high northern latitudes, the warming trends are more pronounced in the spring and are also evident in summer and fall, resulting in a longer melt season for snow and ice on land and for annual sea ice.

Satellite data also show that the portion of the Arctic Ocean covered by perennial sea ice has declined by about 9% per decade since 1978. The longer melt season and loss of perennial sea ice cover can have large-scale climate consequences. They permit an increase in the amount of energy absorbed in the previously ice- or snow-covered areas and, on land, permit increased growth of vegetation that also has a lower a (lower light reflectivity) than snow covered areas.

Climate models project that the high latitude regions are particularly sensitive to climate change because of the positive albedo feedback effects associated with reduction of ice and snow cover, and the reduction of thermal insulation of the ocean that sea ice cover provides, allowing increased heat transfer from the ocean to the atmosphere. However, there is as yet no direct evidence that greenhouse gas forcing, which drives the climate models, is responsible for the melting of sea ice and snow cover in the Arctic region.

The data also show regional differences that suggest there are other influences in addition to global-scale climate warming. A natural weather pattern called the North Atlantic Oscillation/Northern Annular Mode (NAO/NAM) may have contributed to regional variations as well as the overall decrease in Arctic sea ice cover over the last 20 years. Whether the ice cover as a whole will continue to exhibit the decreases that it experienced over the 1979 to 2003 period might depend on the strength and phase of the NAO/NAM, as well as on long-term trends in the climate system. (See Figures 8a and 8b)

Increasing ocean heat storage:

Simulations with an improved version of the NASA/GISS Global Climate Model indicate that the rate of heat storage by the world’s oceans has increased from about 0.2 watts/m² in 1951 to a present value of about 0.7 watts/m² net downward flux (convergence) of heat into the ocean surface. This is the third independent climate model to produce such an increase, and compares well with observational analyses of changes in ocean heat storage. Since the ocean stores a large portion of the excess heat due to the imbalance of the radiation budget of the Earth’s climate system, this work indicates that careful monitoring of the global distribution of ocean heat storage will be a key indicator for identifying changes in the climate system.

Change in the freshwater balance of the Atlantic Ocean:

The distribution of salinity in the Atlantic Ocean has been sampled over a broad area during the last half-century. These historical data can be used to diagnose rates of surface freshwater fluxes, freshwater transport, and local ocean mixing — important components of climate. Recent research comparing observed salinities on a long transect through the western basins of the Atlantic Ocean between the 1950s and the 1990s found systematic increases in freshwater at high latitudes (at both poleward ends), contrasted with large increases of salinity at low latitudes. Although the observational record is insufficient to quantify a number of factors that may have contributed to these long-term trends, a growing body of evidence suggests that shifts in the oceanic distribution of fresh and saline waters are occurring in ways that may be linked to global warming and possible change in the global water cycle. Parallel changes in ocean salinity and temperature are occurring in other oceans as well.

20th Century global sea-level rise:

The rate and causes of 20th century global sea-level rise are subjects of intense debate. Direct observations, based on tide gauge records suggest that the rate of sea-level rise is between 1.5 and 2.0 mm/year (0.6 to 0.8 inches/decade). The two largest contributors to sea-level rise are thought to be volume changes due to ocean warming (thermal expansion) and the addition of mass due to the melting of polar ice sheets, although the magnitudes of these contributions are not well known. Scientists at NOAA’s Laboratory for Satellite Altimetry analyzed tide gauge records, which reflect both volume and mass changes, and ocean temperature and salinity data, which reflect only volume changes, in the North Pacific and North Atlantic Oceans. They found that measurements of sea-level rise from tide gauges are 2-to-3 times higher than those from temperature and salinity measured regionally and near gauge sites. The data support earlier estimates of the 20th century rate of sea-level rise and, more importantly, also provide the first evidence suggesting that addition of mass due to the melting of polar ice sheets can play an important, perhaps dominant, role in sea-level rise.

Simulating 20th century climate:

Multiple ensemble simulations of the 20th century climate have been conducted using climate models that include new and improved estimates of natural and anthropogenic forcing. The simulations show that observed globally averaged surface air temperatures can be replicated only when both anthropogenic forcings, e.g., greenhouse gases, as well as natural forcings such as solar variability and volcanic eruptions are included in the model. These simulations improve on the robustness of earlier work. Comparisons of the model results with observations indicate that regionally concentrated increases in precipitation can occur as a function of variability in solar forcing. (See Figure 9)

Detecting a human influence on North American climate:

A recent study shows that the average global results reported above also pertain over the North American region. Several indices of large-scale patterns of surface temperature variation were used to investigate climate change in North America over the 20th century. The observed variability of these indices was simulated well by several climate models. Comparison of index trends in observations and model simulations shows that North American temperature changes from 1950 to 1999 were unlikely to be due only to natural climate variations. Observed trends over this period are consistent with simulations that include anthropogenic forcing from increasing atmospheric greenhouse gases and sulfate aerosols. However, most of the observed warming from 1900 to 1949 was likely due to natural climate variation.

Long-term drought reconstructions for North America:

Tree-ring paleo-proxy records have been used to develop an animated atlas of North American drought for the last ~1,000 years. The data show annual (and even within-year) resolution of drought/wetness conditions across the United States and parts of Mexico and Canada. This synthesis provides a dramatic visual representation of changing climatic and environmental conditions over the region, including an indication that significantly more arid conditions existed in parts of the western United States prior to AD 1500. Such paleoclimate data help aid the understanding of climate mechanisms and impacts.

Origins of recent severe droughts in the Northern Hemisphere:

Recent work provides compelling evidence that severe droughts that affected the United States, the Mediterranean region, and Southwest Asia simultaneously during 1998-2002 were part of a persistent climate state that was strongly influenced by the tropical oceans. The oceanic conditions of importance were unusually cold sea surface temperatures (SSTs) in the eastern tropical Pacific, i.e., persistent La Niña conditions, that occurred together with sustained above normal SSTs in the western tropical Pacific and Indian Oceans. The persistence of this abnormal tropical SST pattern was unprecedented in the instrumental record. A large suite of model simulations showed that this SST pattern was ideally suited to force atmospheric circulation anomalies that were conducive to producing abnormally dry conditions in those regions where severe and sustained drought was observed.

Causes of the 1930s Dustbowl:

A NASA atmospheric general circulation model was used to investigate the North American dustbowl drought during the 1930s. Ensemble simulations using observed sea-surface temperatures (SSTs) show that principal causes of the Great Plains drought were the anomalous tropical SSTs during the 1930s in the Pacific and, to a lesser extent, the Indian and Atlantic Oceans. Land-surface feedbacks were also essential to the development and maintenance of the severe drought conditions.

Role of stratosphere:

Recent observational analyses suggest that, together with the tropical oceans, the stratosphere increases the ‘memory’ of the climate system, and also may influence long-term variations in the polar ice pack, sea surface temperatures, and the deep ocean circulation. This stratosphere-troposphere connection has important implications for the prediction of the response of tropospheric climate under increasing concentrations of greenhouse gases. Currently, sophisticated climate models differ as to whether the stratospheric polar vortex, a key part of the connection, will strengthen or weaken with increasing concentrations of greenhouse gases.

Role of aerosol infrared forcing:

A crucial factor limiting the predictability of global climate is the large uncertainty about the precise effects of aerosols on Earth's radiation balance. Most large-scale global climate models include the direct radiative effects of aerosols at higher wavelengths, but few consider aerosol radiative properties in the infrared (IR) region. Measurements of clear-sky IR spectra, performed during a cruise across the western Pacific Ocean, revealed aerosol forcings of up to 10 W/m². These values are quite large compared to the 1-2 W/m² forcing estimated for greenhouse gas accumulations since the beginning of the industrial revolution. Based on these measurements and analyses, aerosol IR effects will be included in the next version of the National Center for Atmospheric Research (NCAR) Community Climate System Model.

Effects of Indo-Pacific ocean mechanisms:

A new multi-year assimilation of in-situ and satellite data into an ocean model highlighted the importance of the interior ocean mechanisms (as compared to boundary currents such as the Gulf Stream) on timescales of weeks to months. Investigators found these mechanisms in the interior ocean play a critical role in altering the water mass exchanges between the midlatitude eastern Pacific Ocean and the the tropical Pacific where El Niño develops, suggesting that remote effects on El Niño should be more carefully considered by prediction models. Further, these relatively fast mechanisms were found to govern more generally the transports and exchanges between the tropical and midlatitude ocean and thus could be an important factors for observing and modeling the longer-term changes (e.g., interannual to decadal variability) of the Pacific Ocean.

Diagnostic for Evaluating Climate Model Performance :

Scientists developed the Broadband Heating Rate Profile (BBHRP), a new model diagnostic that will help reduce a significant obstacle to improving the predictive accuracy of climate models—the ability to accurately quantify the interaction of the clouds, aerosols, and gases in the atmosphere with radiation. Because direct observation of these interactions is extremely difficult, there has been no observation standard with which to compare and judge the accuracy of climate model simulations. The BBHRP, which is based on an assimilation of detailed field measurements from the Atmospheric Radiation Measurement program, provides a realistic estimate of radiative heating or cooling impact of clouds, aerosols, and gases. This diagnostic can be directly compared to the model-predicted impacts, thus enabling model uncertainties to be evaluated.

Highlights of Plans for FY2004 and FY 2005

The CCSP will continue to enhance observational and modeling capabilities for improved understanding, prediction, and assessment of climate variability and change on all timescales. Climate Variability and Change modeling activities will be linked with the CCSP climate modeling strategy. 

Key climate modeling research plans for FY 2004 and FY 2005 include:

Continue development of next generation climate models:

Work is underway to develop the next generation of global climate models at the major modeling centers in the United States. The research will produce improved representation of physical processes, e.g, convection and clouds, and more complete and improved representations of coupled interactive atmospheric chemistry, terrestrial and marine ecosystems, biogeochemical cycling, and middle atmospheric processes. This work is being initiated in FY 2004 and will be ongoing in FY05.

These activities will address Goal 1 of the CCSP modeling strategy.

Improve climate model evaluation and modeling infrastructure:

Infrastructure for major model evaluation and improvement will be provided, coordination of model intercomparisons will be conducted, and model testbeds for parameterization testing will be maintained by the DOE Program for Climate Model Diagnosis and Intercomparison. A major effort will be dedicated to providing a robust and extensible software engineering framework for the Community Climate System Model, a code used by hundreds of researchers on many different high-end computing platforms. This work is now underway and will continue in FY 2005.

These activities will address Goal 1 of the CCSP modeling strategy.

Enhance computer capabilities at Geophysical Fluid Dynamics Laboratory to support the Climate Change Technology Program (CCTP):

The NOAA Geophysical Fluid Dynamics Laboratory (GFDL) supercomputing capability will be enhanced in FY 2004 to enable additional climate projections for research and assessment based on emissions scenarios developed through the CCTP. Likely case studies will include exploring the range of plausible future environmental consequences of different emission rates resulting from combinations of new technologies.

These activities will address Goal 2 of the CCSP modeling strategy.

Perform multi-century simulations and projections for the IPCC Fourth Assessment Report:

Scientists at GFDL, NCAR, and six DOE National Laboratories will complete the production of ensemble multi-century global simulations and projections of climate variability and change for use in the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report. Some of these simulations will be modeled at twice the resolution used in the past in order to provide more useful information for downscaling results to regional scales. This, in turn, can enhance the capability of climate impacts scientists and other researchers to produce environmental information to support informed resource management and policymaking. This work will begin in FY 2004 and continue through FY 2005.

These activities will address Goal 3 of the CCSP modeling strategy

Further implement the Earth System Modeling Framework:

The Earth System Modeling Framework project will be enhanced and will produce initial climate simulation experiments in FY 2004, continuing through FY 2005. Several existing ocean and atmospheric models from NASA, NOAA, NSF, DOE, and university labs will be connected and coupled to produce new prototype modeling systems. This is a major milestone to enable full interoperability among atmosphere, land, ocean, and other models to improve the fidelity and predictive capability of the models.

These activities will address Goal 3 of the CCSP modeling strategy.

Key observations and process studies research plans for FY 2004 and FY 2005 include:

Continue research by Climate Process and Modeling Teams (CPTs):

DOE, NASA, NOAA and NSF have jointly initiated three Climate Process modeling Teams (CPTs). The CPTs are focusing their research on cloud feedbacks and ocean mixing, high-priority climate processes that are responsible for climate model deficiencies and thus uncertainties in climate change projections. This work will continue through FY 2005.

 These activities will address Question 4.1 and modeling strategy Goals 1 and 3 of the CCSP Strategic Plan.

Assess aerosol impact on cloud and water vapor feedbacks and climate change:

A focused research effort on the aerosol impact on cloud-radiation feedback and climate change will be initiated by coupling atmospheric chemistry, radiation science, and global modeling. The focused effort, which will continue through FY 2005, will develop improved representations of the aerosol impact on cloud and water vapor feedback processes in climate models. (This is a collaborative effort with the CCSP Global Water Cycle research element.)

These activities will address Question 4.1 of the CCSP Strategic Plan.

Assess impact of climate forcings on long-term climate change:

NASA's Goddard Institute for Space Studies (GISS) will systematically change the climate forcings in its modeling experiments to evaluate the relative impact of climate forcings on long-term climate change and to understand the climate sensitivities to the various forcings. This research, initiated in FY 2004 and continuing until at least FY 2006, is an important step in building capability to provide answers to "if...then" questions relevant to resource management and environmental policy.

These activities will address Questions 4.1 and 4.2 of the CCSP Strategic Plan.

Improve subsurface ocean observations:

The international Argo collaboration will establish a global network of free-drifting floats equipped with sensors for measuring the temperature and salinity of the upper 2000 meters of the oceans. Argo will allow, for the first time, continuous monitoring of the climate state of the oceans, with all data being relayed and made public within hours after collection. Data from the Argo floats will be used both operationally and in climate research programs. Argo float deployments began in 2000 and will continue during FY 2004 and FY 2005, with completion of the full array to be achieved over the next several years.

These activities will address Questions 4.1 and 4.2 of the CCSP Strategic Plan.

Obtain new high-density global observations of atmospheric temperature and water vapor:

The United States — with participating agencies NSF, DOD (Space Test Program, U.S. Air Force, U.S. Navy), NASA, and NOAA — in partnership with Taiwan, will launch six low Earth orbit (LEO) satellites, each carrying a set of instruments designed to measure high-resolution vertical profiles of atmospheric temperature and water vapor. This Constellation Observing System for Meteorology, Ionosphere and Climate project (COSMIC) will provide approximately 3,000 vertical soundings per day, uniformly distributed over the globe. This will be an improvement over the current global radiosonde network of balloon-borne instruments, especially over the oceans and polar regions. The current system, which is the mainstream observational network for operational weather and climate prediction and research, obtains about 600 soundings twice a day. COSMIC will complement rather than replace the current system. Launch is scheduled for September 2005.

            These activities will address Questions 4.1 and 4.2 of the CCSP Strategic Plan.

Develop assimilated long-term global ocean circulation data set:

Researchers working on the Estimating the Circulation and Climate of the Ocean (ECCO) project, formed under the National Ocean Partnership Program (NOPP), will initiate the production of assimilated decadal ocean data product at near eddy-resolving scale (1/4 degree) in FY 2004. The work in analyzing the data will continue into FY 2005.

These activities will address Question 4.2 of the CCSP Strategic Plan.

Continue research on thinning and acceleration of sensitive glaciers in Antarctica:

Satellite radar data have shown that the area around the Thwaites and Pine Island Glaciers, known as the "weak underbelly of the West Antarctic Ice Sheet," has experienced thinning in recent years in a manner that is consistent with observed glacier acceleration. This thinning appears to be contributing to sea-level rise, but the extent to which the ice sheet as a whole is influencing sea level has yet to be accurately assessed (given the large spatial variability of this thinning and observed thickening of ice in other regions). NASA's Ice Cloud and Land Elevation Satellite (ICESat), which was launched in January 2003, is expected to help provide a reliable estimate of these changes. Analysis will continue through FY 2005.      

These activities will address Question 4.2 of the CCSP Strategic Plan

Provide new Arctic paleoclimate products:

Based on a new synthesis of data from the Holocene Thermal Maximum (~9,000 years ago), warming is asynchronous and asymmetric across the North America Arctic region. Warming begins in the west and sweeps eastward. A georeferenced database of annually resolved records of Arctic temperature over the past 1,000 years is under development and is scheduled for completion and on-line availability in late FY 2004. Such maps, data, and manuscript references will provide spatially-detailed information about Arctic temperature trends over the last millennium, which can be used to compare more recent changes with the patterns of change from the mid-Holocene geologic epoch.

These activities will address Questions 4.2 and 4.3 of the CCSP Strategic Plan.

Perform deep time paleoclimate research:

Researchers supported by NSF, along with researchers at NASA and USGS, have begun a multi-year data analysis and climate modeling effort to create 3-dimensional global data sets of middle Pliocene epoch (~ 3.0 million years ago) ocean temperature and salinity. This will create the most comprehensive global reconstruction for any warm period of Earth's climate prior to the most recent past. Estimates of middle Pliocene global warming suggest that temperatures were approximately 2oC greater than today. This level of warming is within the range of projected global temperature increase in the 21 st century. No other time period in the past 3 million years approaches this level of warming. Analysis of this period challenges the science community's understanding of the sensitivity of key components of the climate system and how the system is simulated, i.e., polar vs. tropical sensitivity, the role of ocean circulation in a warming climate, the hydrological impact of altered storm tracks, and the regional climate impacts of modified atmospheric and oceanic energy transport systems.

These activities will address Question 4.2 and 4.3 of the CCSP Strategic Plan.

Key decision support resources development activities for FY 2004 and FY 2005 include:

Report on understanding of vertical temperature trends:

A CCSP synthesis report on understanding and reconciling differences in observed temperature trends in the lower atmosphere will be produced for publication in FY 2005. In October 2003, 55 scientists from academia, the U.S. Government, and several other countries participated in a workshop at the National Climatic Data Center on the current state of knowledge and scientific uncertainties on this subject. Follow-on activities will include coordination with a workshop to be held at the UK Hadley Centre in June 2004. A solid foundation has been laid to proceed with the delivery of a synthesis report, with NOAA as the lead CCSP agency and DOE, NASA, and NSF contributing.

This activity will address Questions 4.1 and 4.5 of the CCSP Strategic Plan.

Develop, evaluate, and provide new probability forecasts of seasonal climate anomalies resulting from ENSO:

In FY 2004 and FY 2005 major R&D efforts will continue on improving probabilistic intra-seasonal to interannual climate forecasts, and on developing new and improved climate forecasting products with regional and sectoral applications to water resource management and agriculture.

This activity will address Questions 4.4 and 4.5 of the CCSP Strategic Plan.

Provide improved climate information products for resource management:

Regional integrated research will develop climate information products in FY 2004 and FY 2005 for the agricultural, wildfire, and water management sectors.

These activities will address Questions 4.4 and 4.5 of the CCSP Strategic Plan.