Environmental change in the Eastern Mediterranean and Middle East (EMME)
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 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 onto the latest generation high-performance computers. By using this computer model system in combination with meteorological data and satellite observations we have shown 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 unusually strong positive surface temperature and negative rainfall trends in the EMME in recent decades. Model simulations that compare scenarios with and without increasing greenhouse gas and aerosol emissions, supported by observations, 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, together 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 commonplace by the middle and the end of the century.
Advancements in climate modelling
Within C8 major advancements have been achieved in the representation of aerosol particles, including desert dust, and pollution related processes in our atmospheric chemistry – climate model (CCM). In computing the climate effects of aerosol particles, their water activity is a key factor in aerosol thermodynamics and hygroscopic growth. We have introduced a new representation of water activity that is also valid for cloud condensation nuclei (CCN) activation, hence for both sub- and super-saturated conditions.
Our CCM uniquely accounts for aerosol number, size and composition, and their effects on particle growth by water uptake and cloud droplet formation. In support of previous model predictions, we found that pollution aerosols generally increase the cloud droplet concentration of low level clouds, hence the cloud optical thickness (reflectivity), and prolongs their lifetime, which exert a radiative cooling forcing on climate.
Using the newly developed aerosol microphysics and chemistry submodels we performed the first global computations of aerosol hygroscopicity. In a pre-industrial scenario, the hygroscopicity was higher over marine regions and lower over the continents, because the anthropogenic particulate matter is less hygroscopic than sea spray but more hygroscopic than the natural continental background aerosol (dust and organics). In regions influenced by desert dust the particle hygroscopicity has increased strongly by the mixing with air pollutants.
We developed a submodel to describe organic aerosols and their chemical ageing in the atmosphere. It simulates the formation of secondary organic aerosol and distinguishes compounds from different source and volatility categories. Further, we developed a submodel to account for different particle mixing states, and showed that the global aerosol direct radiative forcing for homogeneous internal mixing (most realistic) differs strongly from that for external mixing (most applied).
We introduced a new submodel for dynamic dust emissions that accounts for soil texture and cation mineralogy of deserts worldwide, and showed that mineral dust has a major impact on the concentrations of semi-volatile pollutant gases. Dust in the atmosphere increases the global nitrate concentration by >40%. Using a high-resolution regional model as a downscaling tool, we learned that over the EMME dust enhances the formation of ice crystals in winter storms, leading to small shifts in precipitation patterns. However, the total amount of precipitation in the region changes little. We did not find evidence for changes in the intensity of rain events in the region.
Our CCM consistently simulates aerosol microphysics and chemistry effects on particle hygroscopic growth and droplet nucleation. We found that globally, small Aitken particles are a large source of CCN. Although in polluted regions larger aerosols (accumulation size) typically overwhelm Aitken particles, in a large part of the atmosphere the latter are still important. Since for small particles the chemical composition is more critical than for large, dilute aerosols, we found significant sensitivity of cloud droplet formation to aerosol chemistry.
Impact of South Asian monsoon of EMME
The summer circulation over the eastern Mediterranean is dominated by persistent northerly winds (Etesians) whose ventilating effect counteracts the adiabatic warming induced by large-scale subsidence. Both these circulation features appear to be reconciled manifestations of the South Asian monsoon influence. In late spring a westward expanding upper level warm structure and subsidence are associated with Rossby waves excited by the monsoon convection. The pronounced topography modifies the monsoon induced structure, firstly by inducing orographically locked summer anticyclones, and secondly by amplifying the subsidence and the northerly flow.
Our analysis of long-term meteorological data revealed a linkage between the South Asian summer monsoon and troposphere-stratosphere interactions (tropopause folding activity) over the eastern Mediterranean. We found that the monsoon governs the interannual variability of subsidence of the EMME as well as tropopause folds. An upward trend in fold activity was identified, especially in the month May. This was attributed to the recent advanced monsoon onset and the deepening convective activity throughout summer, which promotes upper-level baroclinicity over the region and favors tropopause folding. The upward trend in tropopause foldings over the EMME can increase ozone concentrations in the lower atmosphere.
Airborne desert dust mixes with air pollution
Interactions of desert dust particles with air pollution over the EMME, i.e., dust ageing, have been studied with our advanced CCM. It was 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 its concentration. Since aerosol particles cool the Earth surface by backscattering of solar radiation, the enhanced removal of dust can regionally contribute to climate warming.
In strongly polluted and dusty regions the highly efficient coating of dust by pollution acids provides a predominant source of CCN. The pollution-enhanced activation of dust particles into droplets is remarkably efficient so that under highly polluted conditioned haze-clouds can even form below 100% relative humidity. Contrary to previous analyses, we found that the haze particles influence the spectral shape of the cloud droplet size distribution such that the indirect climate cooling effect of aerosols on clouds is increased. Widespread haze in the most strongly polluted regions of the world, in combination with low-level cloud formation, can exert an unexpected strong regional cooling forcing on climate.
Our long-term CCM simulations, combined with satellite observations, indicate that downward aerosol optical depth (AOD) trends over the US and Europe are related to declining pollution emissions, while in the Middle East meteorological changes play a major role in upward AOD trends. When the surface temperature increases over dry desert soils, relative humidity decreases, which promotes dust mobilization. Decomposing the regional trends into aerosol types reveals that the soluble components are the most dominant contributors to AOD, as their influence is enhanced by aerosol hygroscopic growth.
Air pollution, climate change and public health
In the Middle East during summer ozone mixing ratios can reach a pronounced maximum. Using our CCM in combination with satellite data we showed that especially in the Persian Gulf region conditions are highly favorable for ozone air pollution. Our results indicate that the region is a hot spot of photochemical smog where air quality standards are violated throughout the year. Long-distance transports of air pollution from Europe and the Middle East, natural emissions and stratospheric ozone conspire to bring about relatively high background ozone mixing ratios. This provides a hotbed to strong and growing indigenous air pollution in the dry local climate.
In collaboration with public health specialists, high-resolution CCM model calculations have been used to compute mortality attributable to air pollution by ozone and fine particulate matter (diameter <2.5µm). The global model output was combined with epidemiological concentration-response functions to estimate mortality by lung cancer, respiratory and cardiovascular diseases. Airborne desert dust was estimated to lead to about 400,000 premature deaths per year, being mostly natural, largely in North Africa, the Middle East and some parts of Asia.
Anthropogenic air pollution effects on human health were found to be strongest in South and East Asia. Scenario calculations for the coming decades suggest that especially in countries with many megacities strong air quality control measures will be needed to prevent dramatically increasing mortality. We estimated mortality attributable to air pollution in the year 2010 at 3.3 million (including desert dust), which could double in 2050 unless effective air pollution control measures will be implemented.
Using population, medical and meteorological data in Cyprus a clear relationship between high temperatures and cardiovascular mortality was established; this relationship was intensified on heat wave days. The results were consistent regardless whether the minimum, maximum, or mean temperatures were used, although the association seemed to be more pronounced with the mean temperatures, which suggests that consecutive high day- and night-time temperatures are the most hazardous for human health.
Atmospheric signs of crisis observed from space
Using satellite observations of tropospheric NO2 and a number of economic metrics, we investigated the impact of the economic crisis (from 2008 onward) on air quality in Greece, and Athens in particular. The multiannual analysis, supported by ground-based measurements, showed that nitrogen dioxide (NO2) concentrations in Athens have reduced by 30-40%. The declining concentrations of a range of pollutants, however, are associated with an increase in ozone due to reduced titration by NO. The strong correlations between pollutant concentrations and monetary indicators show that the economic recession has resulted in proportionally lower levels of pollutants in large parts of Greece.
The Middle East is a region that receives much attention with upheaval and armed conflict. Environmental changes have not been in the center of public attention, however, they are also remarkable. We found that there are clear links between the two. We detected air pollution trends in the Middle East since 2005, based on satellite observations of NO2 and sulfur dioxide (SO2). Nitrogen oxides are important because they cause ozone pollution, and along with SO2 they also form aerosol particles. We found that the space measurements of air pollution help monitor environmental controls; but also the impacts of economic crisis, armed conflict and the related mass migration of people.
In Syria and Egypt, uprisings and political crises have been associated with strongly declining air pollution since 2011. While in Syria the flows of refugees have reduced air pollution, it has rapidly increased in Jordan, and especially in Lebanon. Also in central Iraq, where the Islamic State is active, air pollution declined. In Iran, sanctions by the UN Security Council were extended sharply in 2010. Since then a strong drop in air pollution has occurred, also from tanker ships in the Persian Gulf, indicating a decline of oil export.
Air quality, climate change and impacts in the 21st century
We performed a comprehensive climate assessment, concluding that the EMME is likely to be greatly affected by climate change, associated with increases in the frequency and intensity of droughts and hot weather conditions. We analyzed long-term meteorological datasets along with high resolution climate model projections for the 21st century. This suggests a continual, gradual and relatively strong warming of about 3.5–7°C between the 1961–1990 reference period and the end of the century. Daytime maximum temperatures appear to increase most rapidly over the Balkan Peninsula and Turkey. Hot summer conditions that rarely occurred in the reference period may become the norm in future.
High resolution climate model calculations have been performed to assess the risks of extreme weather conditions in the EMME. We found that across the Balkan Peninsula and Turkey climate change is particularly rapid, and especially summer temperatures will increase strongly. Temperature rise is amplified by the depletion of soil moisture, which limits evaporative cooling, prompted by the waning of large-scale weather systems that generate rain. Very hot summers that occurred only rarely in the recent past are projected to become common by the middle and the end of the century. Throughout the region, the annual number of heat wave days may increase drastically.
The likely effects of climate change on the water resources in the eastern Mediterranean and Middle East have also been investigated. Our results suggest a 10-15% decline in precipitation across the region by the middle of the century, with considerable variation between countries and river basins. It is expected that per capita water resources will not change significantly in southeastern Europe, where water is relatively plentiful and population growth is minimal. However, in much of the Middle East, climate change and population growth are expected to strongly reduce per capita water resources. This will likely result in social, economic and environmental challenges in the region. For example, our results indicate that for the recent period the highest wheat yields are found in the Fertile Crescent and the coastal areas of eastern Mediterranean Europe. The former region is projected to be negatively affected by climate change, while in the latter region yield gains may be expected.
We used our CCM in scenario studies to estimate the impact of anthropogenic emission changes on global and regional air quality in the recent past and the near future (2025 and 2050). To identify hot spots of poor air quality, a multi pollutant index (MPI), suited for global model output, has been applied. It appears that East and South Asia and the Middle East represent such hotspots due to very high pollutant concentrations. In East Asia a range of pollutant gases and fine particulate matter is projected to reach very high levels in the near future, while in South Asia air pollution will grow rapidly towards the middle of the century. In the Middle East, where natural aerosol concentrations are already high (desert dust), ozone levels are expected to increase strongly.
We used high resolution climate model simulations to assess the risk of forest fires on global, regional (EMME) and local (Cyprus) scales. We applied a fire weather index to weigh the components that contribute to fire risk. It was found that during boreal summer the USA, South and Central Asia and Africa are the most fire sensitive regions. Relatively high fire risks are also found for the Mediterranean. Increases in fire risk are expected in Italy, the Balkans, Greece, Cyprus and Turkey.
Climate change can also influence the transmission of vector-borne diseases through altering the habitat suitability of insect vectors. We performed high-resolution global climate simulations, and collaborated with infectious disease biologists to evaluate factors that may affect the distribution of the Asian tiger mosquito (Aedes albopictus), which transmits pathogens that cause chikungunya, dengue fever, yellow fever and various encephalitides. From the climate projections for 2050 we estimated that approximately 2.4 billion individuals in a land area of nearly 20 million km2 will potentially be exposed to Ae. albopictus.