Is there a relation between extreme weather and antropogenic climate change?

  • Change in probability of heavy precipitation and hot extremes. Credit: E. M. Fischer and R. Knutti. Nature Climate Change

  • Is there a relation between extreme weather and antropogenic climate change?
    09.05.2015 14:01

    On the 6th of May, it was announced by the National Oceanic and Atmospheric Administration (NOAA) that for the first time since they started tracking carbon dioxide in the atmosphere, the monthly global concentration of this greenhouse gas surpassed 400 parts per million in March 2015. This will ensure further global warming over the coming years, despite natural variability. Coincidently, on the same day as the announcement a tornado hit northern Germany which is another example of extreme weather this year. The question is though: Is global warming and extreme weather related?

    First of all, it is better to make clear that a single event such as this tornado cannot be attributed to climate change. However, some scientific research has shown the increasing chance of more extreme weather as the Earth warms. In fact, some papers published over the last few years in Geophysical Research Letters, Nature and Climate Change have discovered a link between extreme heatwaves and general global warming. Such studies took into account the 2003 heatwave across Europe, the record summer temperatures in Australia in 2013, the 2010 Russian heatwave and the flooding in England and Wales in autumn 2000. In an earlier article this year, the relationship between more frequent high category hurricanes and global warming was mentioned.

    One of these new findings points to a substantial increase in the likelihood of very warm years over central England. The research, published in Environmental Research Letters, is based on climate models and temperature records for England dating back to 1659. The analysis showed that climate change is clearly visible on the local-scale in this case. Last year, the Met-Office found the same kind of behavior of the weather, showing how climate change has made it more likely to break record temperatures by about ten times.

    More recently, a paper appeared in the Nature Climate Change magazine on the 27th of April showing that climate change provokes changes not only in mean climate but also in extreme events. This is the first to estimate how climate change has favoured some types of extreme event across the globe.  The new study says 75% of extreme hot days and 18% of days with heavy rainfall worldwide can be explained by the warming we've seen over the industrial period. In a future world with 2C warming globally above pre-industrial levels, almost all extreme hot days and 40% of heavy rainfall days will be down to rising temperatures, say the authors.

    What is going to happen with a warming globally of 2°C? Due to the chaotic nature of the atmosphere a linear trend is not expected. Therefore, we are tied to a nonlinear trend which means, for instance, that if we double the current warming of 0.85°C to 1.7°C this does not mean that the percentage of moderate daily precipitation due to global warming will change to 36%. In fact, the results of this research are quite worrying. They claim that, on average over land, at a global warming of 2°C the probability of precipitation extremes increase by about 65% whilst, the probability of hot extremes is double that at 1.5°C warming.

    These events may bring havoc across many countries with huge human, environmental and economical impacts even in developed countries. If we take, for instance, the flooding in south-west Britain last year, it is possible to realise how a rich nation had some difficulties to protect its people from a winter of exceptional rainfall – which may have been caused by less than one degree of global warming, what is going to happen to other nations when they have to face two or more degrees of warming?

    It looks likely that if global warming is going to change nonlinearly then the odds could be more in favour of extreme temperatures, stormy winds and torrential rainfall. However, more research is needed to understand completely the mechanism that brings about extreme weather events and its relationship with climate change. In the meantime, climatologist and meteorologist will continue studying the atmosphere to provide reliable assessments on global risk to improve adaptation and mitigation targets.

    By: Mario Cuellar