Effective Legislation Can Slow Global Warming

Climate change is one of the most controversial topics in modern science. In particular, anthropogenic global warming (AGW) has become a ferociously debated subject in the political arena and in public discourse, despite the overwhelming scientific consensus that humankind’s greenhouse gas emissions have led to significant increases in global temperatures over the last century.  So-called climate change deniers have put forward a plethora of simplistic theories in an effort to disprove the science and find humans not guilty of causing global warming – from solar cycles to El Niño – all of which have been debunked by climate scientists.  One observation has remained a source of inspiration to those hoping to derail AGW – the apparent slowdown in warming since the late 1990s which does not correlate with global carbon dioxide emissions. Now, a team of researchers has used state-of-the-art statistical analysis to not only again confirm that humankind is responsible for global warming, but that we are also the source of this trend-bucking slowdown.

The Study

The study, reported recently by the BBC and National Geographic, used recently developed statistical methods to analyse the properties of trending series, allowing them to examine in detail trends in radiative forcing – the difference in radiant energy received by the Earth and that radiated back into space.  These sophisticated methods meant the authors could home in on trends in anthropogenic radiative forcing – almost entirely caused by greenhouse gas emissions – which correlated well with non-linear trends linking global temperatures  The authors were also keen to point out that climate modelling – much maligned by critics – was not required to analyse the data.

The Outcomes

The analysis allowed close examination of two periods of AGW attenuation which were apparent in the 20^th Century. The dramatic fall in carbon dioxide emissions associated with the prolonged downturn of world economies through WW1, the Great Depression and WW2 actually caused the world to cool, although not enough to offset the rapid increases in temperatures kick-started by the subsequent economic recovery of the 1950s.

The slowdown of the 1990s coincided with reduced atmospheric levels of other greenhouse gases: methane and chlorofluorocarbons (CFCs).  CFCs are extremely potent greenhouse gases, being highly persistent and having warming potencies up to 10,000 times higher than CO2. They became prominent after their extensive use as refrigerants and release into the atmosphere caused a hole in the ozone layer.  The drop in methane levels has been attributed to changed agricultural practices in Asia, whilst CFC levels dropped dramatically after implementation of the Montreal Protocol in 1987, which helped phase out CFCs and other chemicals which damage the ozone layer. As of 2012, 197 countries have ratified the original Montreal Protocol, and levels of ozone depleting chemicals have fallen by 10% from their peak in the 1990s. The authors show that the slowdown of AGW apparent since this time could be entirely accounted for by this drop in CFC levels.

Media Reporting

Given the significance of the study – we are responsible for changing the Earth’s climate, but effective global legislation CAN result in the attenuation of global warming – it has been surprisingly passed over by most news outlets, perhaps because of its reliance on complex statistical analysis.  A cursory search of the Daily Mail website shows its most recent article on AGW discussed the possibility of global warming causing “snakes as long as BUSES and horses shrinking to the size of CATS”. Clearly, effective reporting of such a controversial issue leaves a lot to be desired, despite the huge implications for our future on Earth.

F. Estrada, P. Perron and B. Martínez-López (2013). “Statistically derived contributions of diverse human influences to twentieth-century temperature changes”. Nature Geoscience vol 6, pp 1050-1055: doi: 10.1038/ngeo1999