The human fingerprint on a record hot year

Thursday, Nov 26, 2015, 04:22 AM | Source: Pursuit

Andrew King, David Karoly

Last year was the hottest on record globally. But now 2015 looks extremely likely to break that record – and by some margin.

In a statement from the World Meteorological Organisation (WMO), scientists are also confident the five-year period culminating in 2015 will be the hottest on record.

This year’s strong El Niño in the Pacific (which is normally associated with higher temperatures globally and in Australia) and the background warming related to human-induced climate change are combining to smash the 2014 record.

For the first time, the global temperature will be more than one degree Celsius above the pre-industrial average and the average carbon dioxide concentration will be above 400 parts per million.

2015 continues the trend of warming seen on the global scale (Source: Climate Central)

Climate scientists from the University of Melbourne are working to better understand the factors behind the global record and the impacts on extreme weather events in Australia and other parts of the world.

Professor David Karoly and I are part of the World Weather Attribution (WWA) project, coordinated by Climate Central, investigating the role of human-induced climate change and other factors in these extreme events.

A preliminary analysis of the impending 2015 record by scientists in the WWA project and the University of Reading has quantified the relative influences of the strong El Niño and the background warming trend.

“We estimate the 2015 global temperature anomaly to be 1.05 ºC above the 1850–1900 average that the IPCC takes to be ‘pre-industrial’,” said Professor Karoly.

“Of that 1.05 ºC temperature departure from pre-industrial, roughly 1.0 ºC is due to the anthropogenic forcing (associated with human-caused increases in greenhouse gases in the atmosphere), about 0.05 ºC to 0.1 ºC is due to El Niño and about 0.02 ºC is due to higher solar activity.”

It is clear that without human-induced climate change, 2015 would not be experiencing the record-breaking temperatures.

In fact the kind of anomalies we’re expecting globally for 2015 would be virtually impossible without the influence of humankind on the climate.

Not only will 2015 be the first year to breakthrough the 1 ºC temperature anomaly from pre-industrial climate, it is also the first year in which yearly-averaged carbon dioxide levels above 400 parts per million will have been observed (pre-industrial carbon dioxide levels were about 270 parts per million).

As the concentrations of carbon dioxide and other greenhouse gases rise further we can expect more record-breaking global temperatures in the coming years.

We will also have to get used to hotter weather in Australia, like the record-hot October nationally and in Melbourne, which we can also attribute to the human influence on the climate.

The Cape Grim research station in NW Tasmania collects greenhouse gas data for the Southern Hemisphere.

In recent years there has been a big focus on the “hiatus” in global temperatures. The slowdown in the increase of the globally-averaged temperature came after the very strong El Niño of 1997/98 and its cause has been the focus of a great deal of scientific investigation.

Different analyses have suggested factors such as decadal-scale climate variability originating from the Pacific and reduced solar activity have played a role in the slowdown of global temperature increases.

Nonetheless, the world has experienced several record-breaking hot years since 2000, and 2015 is likely to stand head and shoulders above the 2014 record.

The upcoming Paris talks will determine the action the world takes in tackling climate change. These talks are being held against the backdrop of not only the record-hot global temperatures, but also regional-scale heatwaves that are having increasingly severe impacts.

The path that the world’s leaders decide on in Paris will influence whether we see even more record-breaking temperatures, and their associated impacts, for decades to come.