The Vegetation/Ecosystem Modeling and Analysis Project (VEMAP) is a multi-agency, international collaboration aimed at improving and intercomparing biospheric models for predicting the effects of climate and climate change on terrestrial ecosystems.   Early analysis of results from VEMAP Phase 2 are aimed at understanding the contribution of "ecosystem physiological" responses to terrestrial sinks in the conterminous U.S.  For the period 1980-1993, results from an ensemble of three state-of-the-art ecosystem models agree within 25%, simulating a land carbon sink from direct CO₂ and climate effects of 0.08 gigaton carbon (Gt C) per year. The best estimates of the total sink from inventory data are approximately three times larger (~0.3 Gt C per year), suggesting that processes, such as regrowth on abandoned agricultural land or in forests harvested before 1980, have effects as large or larger than the direct effects of CO₂ and climate. The modeled sink varies by approximately 100% from year-to-year as a result of climate variability, suggesting that any future policy or management measures based on estimates of net carbon storage must take this high temporal variability into account.

A manuscript entitled "What sets the mean transport through Drake Passage," by Peter Gent (OS), William Large (OS), and Frank Bryan (OS) has been submitted to the Journal of Geophysical Research.  The manuscript is an analysis of twelve experiments using the CSM ocean component alone, coupled to a sea-ice model, and in fully coupled CSM mode. The conclusion is that the transport is set mostly by the zonal wind stress or meridional Ekman transport and by the strength of the thermohaline circulation off the Antarctic shelf.  This conclusion is not in agreement with previous hypotheses for what governs Drake Passage transport. It is shown that the transport is definitely not set by the curl of the wind stress at the latitude of Cape Horn.

Three simulations (22K) of the 21st century have been performed using a modified version of CSM.  This version used a fully interactive sulfur chemistry model, and stratospheric ozone concentrations were scaled by the projected amount of reactive stratospheric chlorine.  The first simulation assumed a business-as-usual increase in carbon dioxide concentration.  The second simulation assumed that emission of carbon dioxide would stabilize, such that carbon dioxide concentration would reach its peak just after 2100.  The third simulation was carried out as a part of the Intergovernmental Panel on Climate Change's (IPCC) Third Assessment Report.

The NCAR Paleoclimate Group has improved the PaleoCSM (a low-resolution version of CSM) and performed multi-century, fully-coupled simulations for present-day, pre-industrial times, and the mid-Holocene (4000 BC).  Annual-average, global surface temperatures are 1.3ēC cooler in the pre-industrial simulation compared to the present-day simulation with the largest cooling in the middle- and high-latitude oceans in regions of sea-ice formation.  Ice areas are 10% greater in both polar regions in the pre-industrial run.  Increased summer and early fall insolation at northern middle latitudes during the mid-Holocene leads to delayed sea-ice formation during the fall and a 5% decrease of sea ice annually compared to pre-industrial times.

Aiguo Dai, with Kevin Trenberth and Tom Karl (National Climatic Data Center) explored how the diurnal range of surface air temperature (DTR) is affected by clouds, soil moisture, precipitation and water vapor. The DTR has decreased worldwide during the last 4-5 decades and changes in cloud cover are often cited as one of the likely causes. To learn more click here.