Sunday 23. January 2022
#165 - November


The Physical Science of Climate Change


The latest report from the IPCC confirms its previous findings adding more evidence to the human activity as the dominant cause of the observed global warming.

The Intergovernmental Panel on Climate Change (IPCC) is a major effort by the scientific community to provide evidence to decision makers and the general public on the mechanisms and effects of climate change. This time, 259 authors from 39 different countries worked on a voluntary basis, in line with the IPCC's usual practice, to produce Climate Change 2013: The Physical Science Basis, the first part of the IPCC's Fifth Assessment Report. The major findings are offered in a Summary for Policymakers.

It may be said that the report offers nothing dramatically new. Rather, it confirms previous IPCC reports while adding much more evidence. The IPCC does not do research itself. It is a collaborative work of hundreds of scientists, who review the relevant research of the last few years, and then make their own overall assessment. The main difference between the Climate Change 2007 (IPCC Fourth Assessment Report) and this new report derives from the huge amount of research carried out within this last period, when hundreds of universities and research centres have focused on climate change and related issues.

What follows is a selective summary of the report's findings.


It is now considered even more certain than before (with more than 95% probability) that human activity is the dominant cause of the observed global warming since the mid-20th century. Natural variations, and such natural factors as the sun's own activity, have contributed virtually nothing to warming since 1950. Yet the last 30 years have probably been the warmest for at least 1,400 years.


Forecasts as to future warming up to the year 2100 – using comparable emission scenarios – are little changed from those of in the previous report: in the highest emission scenario, the best estimate of global warming by 2100 remains at 4 degrees Celsius. The rise in sea levels is already faster than in the previous two millennia, and the rise will continue to accelerate – regardless of the emissions scenario. The rise now projected up to 2100 falls within the range of 28-98 cm, as against 18-59 predicted in 2007.


The IPCC expects dry areas to become drier due to global warming, and moist areas to become even wetter. Extreme precipitation events seem to be already increasing in North America and Europe: their intensity is very likely to increase further over most tropical and middle latitudes.

Scientists provide us with the best information they can. It is time for stakeholders (states, companies, NGOs, and civil society) to develop their own perspectives and responses as the forecasts present society with many challenges. International diplomacy and the relevant institutions seem in poor shape: the Copenhagen Summit and the renewal of the Kyoto Protocol are only the most visible failures. The financial crisis dominates the scene, and in opinion polls environmental problems are regarded as non-urgent concern.

In this report, the impact of globing warming on Europe is not described in detail, since there will be further reports on adaptation and mitigation. What is clear is the increased dryness of the Mediterranean area. Heat-wave frequency has increased in many parts of Europe. Yet on the other hand it can be confidently asserted that (in northern and central Europe) floods during and since the 20th century are more and worse than those of the previous five centuries.


At least we can mention two consequences: there will be an increase in the number of people forced to migrate because of the harsh impact of climate change, as droughts and tropical storms will displace millions, being Europe a precise destination. Second, is the threat to Europe's competitiveness: energy prices will increase either if mechanisms for carbon capture are implemented or if there is a decisive switch towards renewable energy sources.

At this stage, it is critical we focus attention and action on what the IPCC Fifth Assessment Report indicates, not least where this transcends strict scientific data. First, the impact of human activity is crucial in our current situation, so that lifestyle changes and civil society engagement are imperative. Second, the most profound task will be that of 'adaptation'. As the report shows, we face significantly changed circumstances: adapting to new and more precarious conditions will stretch the capacities both of individuals and of communities.


Jose Ignacio Garcia SJ





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