?The two regions that respond in a stronger way to global change are the Mediterranean and North Eastern European regions?

Can you briefly introduce your research and the method you used?

I took a number of global model simulations for the 20^th century and the 21^st century. These simulations were carried out by laboratories worldwide and their results are stored in a database in the US and are available for anybody to access. I actually looked at over 150 simulations with 20 different global models for present day climate and future climate (that is climate for the 21^st century) under three IPCC greenhouse gas emission scenarios, called B1, A1b and A2. B1 is a low emission scenario, A2 is high emission scenario, A1b is a medium emission scenario. Then I divided the globe into 26 different regions, only land regions, and I developed a so called Climate Change Index, an index that compares the climate response of different regions with each other to identify which regions respond to a greater extent to global climate change. I call these regions Climate Change Hot-spots. The index is based on four variables, change in average temperature, change in average precipitation, change in temperature interannual variability and change in precipitation interannual variability. I compounded all the information from the 150 plus model simulations for the three scenarios into this one index looking at changes for the last two decades of the 21^st century compared to present day climate measured by the two decades of 1960 to 1980.

What are your conclusions?

Based on this index, which accounts for changes in precipitation and temperature, precipitation variability and temperature variability, I found that the two regions that respond in a stronger way to global change (that is the most prominent Hot-spots) are the Mediterranean and North Eastern European regions. The Mediterranean region is defined essentially as including the Mediterranean countries, the Alps, the southern half of France, the Balkans and Northern Africa. In this region the greatest contribution to the change occurred in the warm season, meaning spring and summer. In the spring and summer the Mediterranean region becomes much dryer in future climate conditions, up to a decrease in precipitation of thirty or forty percent for the highest emission scenarios, and in addition to be much dryer it is also much warmer than average with much increased interannual variability. This means greater swings between very hot and dry summers/springs and relatively wet and cool summers/springs. So to give you an analogy the hot and dry conditions that I found in the future climate simulations are somewhat similar to those found in summer 2003 which you may remember was exceptionally hot and dry, while the relatively wet conditions are closer to those found in the summer 2002. So these future conditions are sort of similar to the swings between these two summers (2002-2003) but with a general drying of the region. The North Eastern Europe region was the other main Hot spot. This region includes the European portion of Russia and Eastern Europe (East of Germany and north of the Black Sea). The main contribution to the climatic change of this region is a large increase in precipitation during the winter season and also a rather large increase in interannual variability. In this case we find more intense storms happening, much increased precipitation and also much increased swings between one winter season and the next. These are the two most prominent Hot-spots. Among other Hot-spots that I would like to highlight is Central America. In the American continent the region that seems to respond the most to climate change is central America, including Mexico and the Central American countries. In this case the main contribution is a large decrease in precipitation both in the dry season and the wet season, along with an increase in interannual variability. These conditions are similar to the ones we have discussed for the Mediterranean region. The reason why I would like to highlight this is that the signal is quite consistent and this region has not been studied much in the past, so I hope that this study would drive some attention to this Hot-spot. Fairly large climate responses are also found in high latitude Northern Hemisphere regions, such as Northern Asia, Northern Europe, Alaska and Greenland. In all these regions the main response is an increase of precipitation, an increase of precipitation variability along with a relatively large warming. Also to highlight is what I call the Southern Equatorial African region, essentially the region that ranges from north of South-Africa to below the Equator. This is also a region that has received little attention in the past but it seems to be quite responsive to global climate change, mostly because if an increase of variability, a phenomenon that is not well understood, at least by me, and that I think requires much more studies. In terms of the regions that responded less to climate change compared to others, I would mention the South American continent, for which, although there are some significant changes in some of the scenarios, the response was relatively low.

Why do you think there is a relatively low response over South America?

I’m not really sure. What I found is that precipitation did not show large changes, so the South American monsoon does not seem to be very responsive to this greenhouse forcing. Of course the region can still undergo large warming in response to global warming but again I’m not sure why this region does not seem to be very responsive to global change. One implication of this is that for this region perhaps other environmental stresses, such as deforestation, can be even more important than global change.

In a letter published in Nature and in an interview for Science at Stake, Gabriel A. Vecchi says that the climate is going toward a more El Nino state. What is your opinion?

I have not looked specifically at this issue in my study, but my personal opinion is that this issues is still under debate, in the sense that it is true that a lot of the models seem to show that global climate would go into a more El Nino-like state but in a recent study it was shown that many of the models that exhibit this response are also the models that are less able to simulate realistic El Nino events in present day conditions. In fact the models that seem more capable of simulating El Nino do not show such a strong El-Nino like response. So I would say that this issue is still open, at least this is my personal opinion.

In the same letter Gabriel A. Vecchi describe human contribution to Climate Change. Based on you research how do you think human activity contribute to Climate Change?

Yes I would definitely agree with this statement, based on most of the detection and attribution studies that I have seen. What essentially these studies do is to compare, for the 20^th century, the model-simulated trends with observed trends and try to separate the different contributions of natural forcings and anthropogenic forcings. Most of these studies do indicate a strong contribution of anthropogenic forcings, particularly in the last 30 or 40 years. The conclusions are different if we look at the first half of the 20^th century where the natural contributions seem to be dominant but definitely in the last 30 or 40 years we can see a very strong imprint of the anthropogenic forcings.

What are the future steps of your research?

One of the focus of my own research is to investigate the uncertainties associated with climate projections, in particular at the regional scale. I think that trying to understand climate change at the regional scale is one of the most important issues in the global change debate because adaptation and mitigation options need to be based on regional information. Until now we didn’t really have much regional climate change information, because not many model simulations were available. The new set of climate change simulations that I have looked at allows us to really have a much stronger grip on the uncertainties and underlying regional change projections and in fact we are actually starting to see some consistent regional signals in different generation global models. Another issue that I think will become increasingly important is the interaction between atmospheric pollutants and climate, meaning the effect of, for example, anthropogenically produced aerosols on the climate system. This is an issue that I think is very uncertain and need to be studied in much greater depth. Another aspect of this interaction, the effect of climate change on air quality, is emerging as an important issue. For example over Europe we are finding that these projected much drier and warmer summer conditions are probably going to induce much higher levels of surface ozone, which can affect human health and can negatively affect ecosystems and crop production. This problem can be very important in other regions with the high levels of pollution, such as Africa or Asia. The last issue I would like to mention concerns the effects of land use changes. There have been several papers which indicated that at the regional scale the effects of land use changes can be as important as, if not more important than, global warming and as you know humans have been changing the land surface very strongly in this century. So these are the three areas I will be focusing on in my future research: uncertainties in regional climate change projections, (two-way) interactions between climate change and pollution, and interactions between climate change and land use change.

Dr. Filippo Giorgi, thank you.