Climate research has made significant progress over the last quarter century, highlighting the extent of the change underway and the part played by human activities in climate change over the last few decades. Awareness of the issues also extends to the general public and politicians. Scientists are now setting about evaluating the rate of global warming and its natural, economic and social impacts. However, advancement of their knowledge is hampered by the uncertainty surrounding core problems, which – because of their great complexity – scientists identify as the ‘grand challenges’ of climate change research. These are not only overarching physical issues (sea-level rise in the world’s oceans, cryospheric processes, etc.) but also questions of how information can be conveyed – or even of how human societies are going to evolve in future.

The probable consequences of global warming are now easy to discern: impoverishment of biodiversity, droughts and flooding, more heat waves, fewer periods of extreme cold, extreme storms. Added to these are indirect effects such as rising sea levels and the faster spread of diseases across larger and larger areas, carried by water and other vectors. Advances in knowledge on these questions are achieved through research into the ‘grand challenges’ of climate change.  This approach can increase the predictive value of climate models and thus contribute to improving dialogue between scientists and decision makers, since government negotiators need precise information in order to take the right decisions. The ‘grand challenges’ of climate science: an overview.

Rising sea levels

The range of possible increases in sea level remains uncertain, since they are strongly dependent on the rate of melting of the Greenland Ice Sheet. Yet there is no doubt that rising water levels bring risks of permanent flooding, which can disrupt the economic activities of major coastal cities, and of increased salt intrusion into coastal aquifers, with negative consequences for soil fertility and therefore for agriculture.

Cryospheric processe

Global warming leads to the melting of permafrost – permanently frozen areas in Earth’s high latitudes and at high mountain altitudes. The consequence of this is uncertainty about the potential increase of carbon in the atmosphere as CO2 and methane are released by organic matter that at present remains frozen within the soils of these areas. Such a release of carbon from permafrost could dramatically increase the greenhouse effect, going beyond the impact of current human emissions.

The role of clouds and aerosols in the climate system

Although it is abundantly clear that clouds play a major role in atmospheric warming and cooling, their role in the climate system is still little understood, since ground-based and satellite-borne measurements have not been able to answer all the pertinent questions, and climate models do not yet have computation grids fine enough to simulate each individual cloud. Particular attention also needs to be paid to measuring and modelling various types of precipitation, since these influence not only surface waters but also the degree of soil moisture, which plays a part in regulating lower atmosphere temperatures.

Access to water

A rise of two degrees can have serious consequences for the melting of polar waters and mountain glaciers. This in turn leads to variations in the quantity of water available for domestic consumption, agriculture or industry, and to possible conflicts of interest between the economic sectors affected – even to conflicts between countries. However, in spatial terms, projections on a scale small enough to facilitate local decision-making are still very rare.

Climate change and extreme events 

The most serious consequence of global warming is extreme weather events: storms, episodes of intense heat or extreme cold, drought, flooding. These events frequently occur in areas of high population density, and consequently are among the most costly economically and in terms of human life. It is therefore vital to determine the precise relationship of cause and effect between climate change and such catastrophes, even though a trend towards increasing frequency and greater intensity of extremes in a warmer climate has not yet been unambiguously established.

In addition to these clusters of physical problems, scientists need to consider questions of how to acquire climate data and how to get their results across to the general public.

Access to climate data

To tackle this issue effectively, there needs to be a focus on setting up compatible databases of information about climate. The relevant data – which are often available only on a fee-paying basis – are designed to meet differing objectives and configured in different formats. In addition, their spatial and temporal coverage varies greatly, and this makes them difficult to use. However, better use could be made of satellite data in order to understand atmospheric, oceanic and cryospheric phenomena.

Regional climate information 

High-resolution spatial and temporal modelling of climate phenomena is essential for economic and political decision-making. But the fact that they are essential does not make them adequate: these types of modelling are generally too crude to be relevant at a regional level, where decisions (on spatial planning, resource use, etc.) are made over timescales varying from a few months to several decades. If advances are to be made in the use of these models, the most recent knowledge about chemical and physical processes must be integrated into them on a continuous basis.

Communicating scientific research to the general public

There has been sustained media interest in climate change issues since the 1990s; yet the same issues have been exploited by industrial lobbies seeking to deny the link between human activities and global warming. The positive aspect of climate change scepticism is that scientists have to refine their knowledge in order to counter criticisms effectively.  More accurate science, using terminology accessible to non-experts, also enables researchers to convince the general public of the reality of the various problems associated with climate change and its impacts, through graphic examples or comparisons that speak for themselves. For instance, a recent study conducted at the ISE illustrated the displacement of climatic patterns from the Mediterranean towards Northern Europe, demonstrating that in 2010, according to temperature and rainfall statistics, Geneva enjoyed the same climate as Toulouse in 1960 and Bordeaux experienced a similar climate to that of Lisbon in the 1950s. Further than this, scientists have to explain clearly why there are uncertainties in their projections for the future – and why, despite these uncertainties, decision-making is possible. And last but not least, the knowledge that scientists convey to the public should also include the predictable socio-economic impacts of climate change, as well as the ethical and legal areas of questioning that these open up.