Final Report Summary - C8 (Consistent computation of the chemistry-cloud continuum and climate change in Cyprus)
Anthropogenic changes of trace gases and aerosol particles in the atmosphere affect clouds, climate, human and ecosystem health and agriculture. The C8 project has addressed these issues with an emphasis on the Eastern Mediterranean – Middle East region (EMME). Major advancements have been achieved in the representation of aerosol particles, including desert dust, and atmospheric pollution chemistry processes in an atmospheric chemistry – climate model, which has been furthered to the latest generation high-performance computers. By using this model in combination with meteorological data and satellite observations we show that the EMME is a global air pollution and climate change “hotspot”.
Our analysis of meteorological and climate proxy data of the past 500 years documents upward surface temperature and downward rainfall trends in the EMME in recent decades. Model simulations that compare scenarios with and without increasing greenhouse gas and aerosol emissions indicate that these trends are anthropogenic. In the EMME climate change is particularly rapid, and especially summer temperatures increase strongly. In temperate and semi-arid areas of the EMME temperature rise is amplified by the depletion of soil moisture, which limits evaporative cooling. Climate change coupled with population growth is likely to reduce per capita water resources considerably. Very hot summers that occurred only rarely in the recent past will become common by the middle and the end of the century.
Throughout the EMME the annual number of heat wave days could increase drastically. Moreover, conditions are conducive for forest fires and air pollution. Our model projections suggest strongly increasing ozone formation, an extra health risk factor to that of the intensifying heat extremes, particularly in urban areas. This adds to the high concentrations of aerosol particles from natural (desert dust) and anthropogenic sources. These environmental stresses in the EMME can have strong health impacts that contribute to premature mortality.
The advanced atmospheric chemistry – climate model uniquely accounts for aerosol number, size and composition effects on particle growth by water uptake and cloud droplet formation. Pollution aerosols generally increase the cloud droplet concentration of low clouds, decrease precipitation and increase cloud water. This extends the cloud cover and lifetime, and hence cloud optical thickness. As a result the Earth's surface cools, which increases atmospheric stability and reduces convective activity. While the global integral of these effects moderates climate warming, on a regional scale it can vary strongly.
During summer the EMME circulation is dominated by persistent northerly winds (Etesians). Their ventilating effect counteracts the warming that is induced by large-scale subsidence, which suppresses cloud formation. These circulation features appear to be tele-connected manifestations of the South Asian monsoon influence. The recent advanced monsoon onset and the deepening monsoon convection throughout summer leads to an upward trend in troposphere-stratosphere interactions (tropopause foldings) over the EMME, which can increase ozone concentrations in the lower atmosphere.
Interactions of desert dust particles with air pollution over the EMME, i.e. dust “ageing”, have been studied with our advanced atmospheric chemistry – climate model. It is shown that large-scale frontal systems enhance dust transport from the Sahara and Middle East. These meteorological systems also carry air pollution from Europe, while the mixing of dust with pollutant gases makes the particles much more soluble. Since the frontal systems also cause rain, the increased solubility and wet deposition remove the dust more efficiently, which decreases the dust lifetime and concentration. Since aerosol particles cool the Earth surface by backscattering of solar radiation, the enhanced removal of dust can regionally exacerbate climate warming.
Our analysis of meteorological and climate proxy data of the past 500 years documents upward surface temperature and downward rainfall trends in the EMME in recent decades. Model simulations that compare scenarios with and without increasing greenhouse gas and aerosol emissions indicate that these trends are anthropogenic. In the EMME climate change is particularly rapid, and especially summer temperatures increase strongly. In temperate and semi-arid areas of the EMME temperature rise is amplified by the depletion of soil moisture, which limits evaporative cooling. Climate change coupled with population growth is likely to reduce per capita water resources considerably. Very hot summers that occurred only rarely in the recent past will become common by the middle and the end of the century.
Throughout the EMME the annual number of heat wave days could increase drastically. Moreover, conditions are conducive for forest fires and air pollution. Our model projections suggest strongly increasing ozone formation, an extra health risk factor to that of the intensifying heat extremes, particularly in urban areas. This adds to the high concentrations of aerosol particles from natural (desert dust) and anthropogenic sources. These environmental stresses in the EMME can have strong health impacts that contribute to premature mortality.
The advanced atmospheric chemistry – climate model uniquely accounts for aerosol number, size and composition effects on particle growth by water uptake and cloud droplet formation. Pollution aerosols generally increase the cloud droplet concentration of low clouds, decrease precipitation and increase cloud water. This extends the cloud cover and lifetime, and hence cloud optical thickness. As a result the Earth's surface cools, which increases atmospheric stability and reduces convective activity. While the global integral of these effects moderates climate warming, on a regional scale it can vary strongly.
During summer the EMME circulation is dominated by persistent northerly winds (Etesians). Their ventilating effect counteracts the warming that is induced by large-scale subsidence, which suppresses cloud formation. These circulation features appear to be tele-connected manifestations of the South Asian monsoon influence. The recent advanced monsoon onset and the deepening monsoon convection throughout summer leads to an upward trend in troposphere-stratosphere interactions (tropopause foldings) over the EMME, which can increase ozone concentrations in the lower atmosphere.
Interactions of desert dust particles with air pollution over the EMME, i.e. dust “ageing”, have been studied with our advanced atmospheric chemistry – climate model. It is shown that large-scale frontal systems enhance dust transport from the Sahara and Middle East. These meteorological systems also carry air pollution from Europe, while the mixing of dust with pollutant gases makes the particles much more soluble. Since the frontal systems also cause rain, the increased solubility and wet deposition remove the dust more efficiently, which decreases the dust lifetime and concentration. Since aerosol particles cool the Earth surface by backscattering of solar radiation, the enhanced removal of dust can regionally exacerbate climate warming.