GC12A-01
From Human Activities to Climate Change: Uncertainties in the Causal Chain
While formal attribution of observed climate change to the overall increase in atmospheric greenhouse gases has been made, the relationship between specific human activities and their consequent levels of climate change has not been followed with the same level of scientific scrutiny. This paper tracks the causal chain from human activities to greenhouse gas emissions as reported under the UNFCCC, to changing atmospheric composition, to radiative forcing, and finally to climate change, propagating a scientific assessment of the uncertainty in climate change caused by those activities. Greenhouse gas emissions for the years 1990 through 2002 are available from most of the Annex-I countries, and we follow the effect these have on atmospheric abundances and global mean surface temperature at the end of the period. A new evaluation of the total aerosol radiative forcing is derived. The probable temperature change in year 2003 that can be attributed to these Annex-I emissions, +0.106 (-0.029,+0.034), is less than half of that due to global emissions for the same period and is asymmetric with a longer tail for larger temperature changes. This study is the collective work of a group of scientists (MATCH) responding to the UNFCCC parties request for scientific evaluation of attributable climate change for possible use in post-Kyoto negotiations.
GC12A-02
Changing Climate, Disrupted Livelihoods: The Case of Vulnerability of Nomadic Maasai Pastoralism to Recurrent Droughts in Kajiado District, Kenya
Pastoralism is practiced in all arid and semiarid lands (ASALs) of Africa. High interannual rainfall variability and degraded ecosystems characterize these ASALs and limits arable farming. Under these conditions, pastoralism has evolved as the most feasible livelihood system in ASALs, where total annual rainfall correlates with annual net primary productivity, especially grass. Maasai of East Africa are the largest group of nomadic pastoralists in Africa, with about two-thirds living in southern Kenya, mainly in Kajiado and Narok Districts. Maasai people of Kenya subsist by nomadic pastoralism. Nomads migrate with their livestock in search of natural pastures and water as climatic and environmental circumstances mandate. Successful migrations of nomadic pastoralists are being hampered by changing social and ecological factors both at local and broader scales. What is more, increased frequency and duration of drought constitute a major challenge with which the Maasai have to confront. Drought is a slow-developing phenomenon; therefore, it captures delayed attention. Nonetheless, the cumulative impacts of drought are more immense. Drought triggers catastrophic events that diminish adaptive capacity of inhabitants of these ASALs; this is conspicuous in Kajiado District where livestock productivity plummet as resource base erodes. What is more, global climate change is projected to intensify the occurrence, severity and duration of droughts in this region. Frequent droughts are likely to disrupt proper functioning of nomadic Maasai pastoralism. This study presents findings from an integrated research conducted in Kajiado District during the last two years. Spatiotemporal trends of drought, effects of drought on, and possible future of nomadic Maasai pastoralism are presented. This is informative to the Maasai pastoralists, policy makers and other actors in this sector. Most important, the study is contributes toward formulation of informed drought management strategies, which in turn may enhance adaptive capacity among the nomadic Maasai pastoralists.
GC12A-03
Assessing the Uncertainty of Future Climate Change Impacts on Terrestrial Wildlife Habitats
The consensus about climate change among scientists is that the global climate is now undergoing a period of rapid change. Because the wildlife management paradigm in the United States places primary responsibility of wildlife resources with individual states, state agencies are in need of information on the magnitude of projected climate change impacts on wildlife habitat and tenable options for ameliorating those impacts. Our research develops that information through reviews of the climate change literature and the State Wildlife Action Plans, and a series of empirical studies that quantify the biodiversity risk associated with changes in wildlife habitat (based on projections from global climate models and dynamic vegetation models). Our index of biodiversity risk attributable to climate change includes climate stress (temperature, precipitation), habitat type and area shifts, changes in habitat quality (via productivity estimates), and proportions of terrestrial vertebrates that are of conservation concern. The index will be used identify ‘hot spots' by ranking areas across the US from high to low biodiversity risk. One of the challenges with addressing the potential climate change impacts on habitat is incorporating an understanding of the uncertainty from the analyses into consequent recommendations. We assess uncertainty by using several climate change projections of temperature, precipitation, productivity and habitat area and developing a synthetic index across these projections, including their variance. The results indicate areas of greatest stress across the US and where variance of the index is minimal, some agreement across the metrics. Using this synthetic index, we identify selected "hotspots" of risk where habitat types and associated wildlife species are at greatest risk from climate change impacts. At this finer scale, we will add to our index the impact of current wildlife movement constraints (land use and cover). From this analysis, we will identify proposed management prescriptions for habitats that have been established in the published literature and compare them with proposed management actions identified in the Wildlife Action Plans. Finally, we will make recommendations to modify proposed actions or identify additional management options that will help minimize climate change impacts to habitat and species.
GC12A-04
Changes of cloudiness over tropical land during the past few decades and its link to global climate change
Tropical forests play a key role in determining the global carbon-climate feedback in the 21st century. Changes in rainforest growth and mortality rates, especially in the deep and least perturbed forest areas, have been consistently observed across global tropics in recent years. Understanding the underlying causes of these changes, especially their links to the global climate change, is especially important in determining the future of the tropical rainforests in the 21st century. Previous studies have mostly focus on the potential influences from elevated atmospheric CO2 and increasing surface temperature. Because the rainforests in wet tropical region is often light limited, we explore whether cloudiness have changed, if so, whether it is consistent with that expected from changes in forest growth rate. We will report our observational analysis examining the trends in annual average shortwave (SW) downwelling radiation, total cloud cover, and cumulus cover over the tropical land regions and to link them with trends in convective available potencial energy (CAPE). ISCCP data and radiosonde records available from the Department of Atmospheric Sciences of the University of Wyoming (http://www.weather.uwyo.edu/upperair/sounding.html) are used to study the trends. The period for the trend analysis is 1984-2004 for the ISCCP data and 1980-2006 for the radiosondes. The results for the Amazon rainforest region suggest a decreasing trend in total cloud and convective cloud covers, which results in an increase in downwelling SW radiation at the surface. These changes of total and convective clouds are consistent with a trend of decreasing CAPE and an elevated Level of Free Convection (LFC) height, as obtained from the radiosondes. All the above mentioned trends are statistically significant based on the Mann-Kendall test with 95% of confidence. These results consistently suggest the downward surface solar radiation has been increasing since 1984, result from a decrease of convective and total cloudiness over the Southern Amazon basin, due to an increase of LFC and atmospheric thermodynamic stability. Such an increase of surface SW radiation probably has contributed to the increasing in growth rate for the forests in the Amazon forests. Currently, the same analysis is being applied using radiosonde data from the Comprehensive Aerological Reference Data Set (CARDS) over the Amazon and Congo basins and the Southeast Asia. Our objective is to identify changes in cloudiness over tropical land and identify its underlying causes, especially the link to changes in surface temperature and humidity.
GC12A-05
Forecasting Ocean Uptake of CO2: A Small Difference Between Large Numbers
It is incredible how well we know present and past carbon cycle budgets (including the ocean uptake of CO2), based on observed atmospheric CO2 time series, emission inventories, and precise isotopic and O/N measurements. But none of these can be used to forecast future oceanic CO2 uptake. Neither can paleo variations: the inhabited Earth has never experienced this much greenhouse forcing. To forecast uptake, we need to compute a small difference between large numbers: about 92 PgC into and 90 PgC out of the ocean annually. The IPCC acknowledges that these gross fluxes are uncertain to 20 percent (at best), but does not note the ramifications of this uncertainy. We show here that as little as a 3 percent change in emission and deposition fluxes (globally averaged over countless regional chemical and physical variations) could double the rate of atmospheric CO2 increase or just as easily change its sign to a net CO2 ocean emission. This is not a forecast, of course, but a simple sensitivity analysis. At the moment we cannot be certain even what the sign of the net ocean CO2 flux will be in a few decades. Most of the research done so far cannot improve on this alarming uncertainty, because past fluxes can not be extrapolated into a non-linear future. This small difference is a very large loose cannon. It is critical that vastly increased attention be given to quantifying the factors that control both exchange velocities and delta-pCO2 values. The goal should be that each factor is well enough quantified that at least the functional form of its impact on exchange fluxes can be incorporated into regionally-specific climate models. Improving exchange velocity models requires the development of instruments that can complement the current LiCor instruments at measuring CO2 fluxes via eddy covariance, with fewer (or at least different) sensitivity and noise problems. Viable options exist.
GC12A-06
Role of Ice Sheets in Thermohaline Circulation Changes Under High Atmospheric Carbon Dioxide Concentration
Thermohaline circulation (THC) changes are considered for two experimental settings of Antarctic and Greenland ice sheets with the atmospheric carbon dioxide of 1200 ppm in GFDL atmosphere-ocean coupled model. The experimental settings are to figure out the role of the ice sheets in global climate system, in which they are present and completely removed. The coupled model consists of the atmosphere and oceans, as well as simple models of land surfaces and sea ice. Atmospheric distribution of predicted variables is represented by Rhomboidal 15 configuration and nine vertical levels. Oceanic variables in 12 vertical levels have horizontal resolution of 4.5 degree latitude and 3.75 degree longitude. Streamfunctions of zonal mean meridional circulation in model oceans are used as representing fields of the THC, which are constructed after reaching statistical equilibrium state at 3000 model years. Same restart file is used for the two runs, which is at approximately 10000 model years of integration with atmospheric carbon dioxide concentration of 300 ppm provided from GFDL/NOAA. The THC appears again, after weakening, strengthening, and rapid-increasing during the first 3000 model years. Analysis periods of the equilibrium state are from 3000 to 10000 model years. Streamfunctions of the two runs show in general similar pattern of circulation cells of North Atlantic Deep Water (NADW) and Antarctic Bottom Water (AABW). The cell of NADW occupies upper 2000 m mainly in north of 10 degree South, but the cell of AABW extends up to 50 degree North from the Antarctic continent in the layer below the deeper part of the NADW, while covering up to the surface in the south of 60 degree South. Difference-field of streamfunction between the two runs shows two core-regions. One core is located in the deeper part of Southern Ocean (i.e., the depth range of 2500-4000 m), and the other in the upper part, 500-2000 m depths, in the Northern Hemisphere. Latitudinal ranges of the two cores are mainly from 30 to 60 degrees. For the present it is conjectured that the two cores in the Northern and Southern Hemispheres of the streamfunction-difference field would represent regional responses to ice sheet removals of Greenland and the Antarctica, respectively. That is, the NADW cell becomes strong, but the AABW cell becomes weak, when the ice sheets are removed. Though the state of oceanic stratification could be the main reason for the deeper presence of AABW cell, the physical mechanism and processes related to the difference field are still under investigation.
GC12A-07
The Southern Ocean response to poleward intensifying winds: a model resolution sensitivity study.
The Antarctic Circumpolar Current (ACC) connects all the major ocean basins, has the highest volume transport in the world ocean and plays a key role in global climate. Observational records and modeling results indicate a consistent poleward intensification of the zonal wind stress over the Southern Ocean concomitant with anthropogenic warming through the 20th and 21st centuries. Coarse resolution global model studies, with simple geostrophic balance considerations, have shown an increase in transport and poleward shift in the position of the ACC in response to the changing winds. However, regional eddy-permitting models identified changes in the intensity of the eddy field but little change in ACC transport (an effect dubbed "eddy saturation"). In this study, versions of a global climate model with horizontal resolutions ranging from 1.8 x 3.6 (degrees) to 0.2 x 0.4 are used to refine our understanding of anthropogenically induced changes in Southern Ocean. The models are forced time-varying Southern Ocean surface wind anomalies through the 21st century. The effect of model resolution on the response of Southern Ocean heat content, volume transport, eddy kinetic energy and heat transport will be discussed. http://www.climate.uvic.ca
GC12A-08
Changes in Global Water Cycle: Discrepancy Between Satellite Observations and Climate Models
Most of the attention on climate change research has been devoted to understanding and predicting surface and atmospheric temperature changes. Changes in the global hydrologic cycle play an important role in impacting the society but they are less understood. The availability of 20 years of a continuous and carefully calibrated satellite data record from the Special Sensor Microwave Imager (SSM/I) provides us with the opportunity to study global changes of variables related to the water cycle: precipitation (P), water vapor (WV), surface winds (U) and derived evaporation (E). The satellite data show that for the past two decades WV, P and E have all changed at the same rate, about 6.5% per degree of warming. This rate of change is expected for water vapor, as dictated by the Clausius Clapeyron equation (C-C), and is also predicted by climate simulations. On the other hand, global P and E are not constrained by C-C, but rather by the atmospheric energy budget. Climate models predict a muted response of the water cycle to global warming, with a P and E increase on the order of 2%/C. This discrepancy between observed and modeled changes to the water cycle needs to be resolved if we want to have confidence in the models and in the observed data record.