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2015 Likely to Be Hottest Year on Record

By Science Media Centre New Zealand

2015 is shaping up to be the hottest year on record, according to the World Meteorological Organization.

This year's global average surface temperature is likely to be the warmest on record and to reach the symbolic and significant milestone of 1° Celsius above the pre-industrial era, according to a statement from the World Meteorological Organization (WMO). This is due to a combination of a strong El Niño and human-induced global warming, the UN agency says.

The years 2011-2015 have been the warmest 5-year period on record, with many extreme weather events - especially heatwaves - influenced by climate change, according to a WMO five-year analysis.

The WMO is issuing the provisional statement on the status of the climate in 2015, and an additional 5-year analysis for 2011-2015, to inform negotiations at the U.N. Climate Change Conference in Paris.

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Prof Martin Manning, Climate Change Research Institute, Victoria University Wellington, comments:

"It seems that Mother Nature is now trying to send some simple round numbers to the United Nations climate policymakers about to meet up in Paris. The predominant greenhouse gas, CO2, is going over 400 ppm for the first time in more than a million years, and surface temperatures are now going over 1°C above preindustrial levels.

"The details are more serious though. Records are being broken even more comprehensively at a regional level for: extremes in temperature, the extent of wildfires, the areas being affected by cyclones, and flooding caused by extreme rainfall. Science is now trying to deal with 1 in 500 year and 1 in 1000 year events.

"Much of this is covered in the latest WMO summary, which is comprehensive but still does not cover everything. More extensive wetlands in the tropics are increasing atmospheric methane. Despite record temperatures in the oceans, the loss of glaciers and ice sheets has now become the predominant driver of sea level rise. And a recent World Bank report has shown that climate related shocks to social systems can lead to irreversible human and physical losses.

"Will policymakers get the message?"

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Dr Karl Braganza is Head of Climate Monitoring at the Bureau of Meteorology, and worked on the WMO report. He comments:

"Typically, global surface temperatures are higher during El Nino years, and the year following an El Nino. With El Nino conditions persisting for the past two years, it is expected that both 2014 and 2015 would have been very warm.2015 has seen record monthly global temperatures for the past six months, with September and October being exceptionally warm.

"Australia is typically very hot over spring and summer during an El Nino, and so far this spring has been no exception. Australia saw record spring temperatures in 2013, again in 2014, and this may well continue for a third consecutive year.

"Currently global surface temperatures are breaking through 1 degree of warming since the pre industrial era, and atmospheric carbon dioxide is breaking through 400 parts per million. These are significant changes for the climate system, with a likelihood that these are the warmest temperatures since before the last ice age, and the highest levels of carbon dioxide in more than two-and-a-half million years."

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Professor Matthew England, Deputy Director of the Climate Change Research Centre at UNSW, comments:

"The global average air temperature record has been absolutely smashed in 2015.

"This warming blows away the record-breaking 1997/1998 El Niño by a massive 0.2 degrees Celsius.

"The cause of this difference between two similar El Niño years is record levels of greenhouse gases in the atmosphere.

"This should be a huge wake-up call in the lead up to Paris for urgent and binding deep cuts in fossil fuel emissions."

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Professor Steven Sherwood, Director of the Climate Change Research Centre at UNSW, comments:

“The most important new circumstance that has emerged is that 2015 stands to become the hottest year ever recorded, probably by a considerable margin, although there is still a bit over one month to go.

"Some have been claiming in the last few years that global warming has slowed, but this new surge of global temperatures leaves these already dubious claims completely in tatters.

"It is not a surprise that global warming continues as strong as ever, because greenhouse gas emissions continue as strong as ever. Only when these emissions are brought to a much lower level will global warming really stop.

"Also, as this report reminds us, the symptoms of global warming, including torrential rains and increasingly severe hot spells, continue as expected.”

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Prof David Karoly is Professor of Atmospheric Science at the University of Melbourne

“Key message: The new record high global temperature in 2015 is mainly due to human-caused global warming, with smaller contributions from El Niño and from other natural climate variations.

"It is now all but certain that 2015 will be the hottest year since record keeping began. Scientists from the World Weather Attribution initiative along with colleagues at the University of Reading performed a simple analysis to assess what factors played a role in this record heat. Specifically, we looked at the roles of greenhouse gas emissions associated with global warming, the natural climate oscillation known as El Niño, as well as solar activity and volcanic aerosols.

"Based on the analysis described in the Methodology section below, we estimate the 2015 global temperature anomaly to be 1.05ºC above the 1850–1900 average that the IPCC takes to be “pre-industrial.” The year 2015 is therefore likely to be remembered as the first year that two symbolic thresholds were set: the 1ºC temperature anomaly threshold and the 400 parts per million (ppm) CO2 threshold.

"Of that 1.05ºC temperature departure from pre-industrial, roughly 1.0ºC is due to the anthropogenic forcing (associated with human-caused increases in greenhouse gases in the atmosphere), about 0.05ºC to 0.1ºC is due to El Niño and about 0.02ºC is due to higher solar activity. The remainder is well within the range of variations due to random weather, especially winter weather in Siberia and Canada. Volcanoes contribute very little at this time.

"El Niño is a relatively small contributor to the record 2015 temperatures because the largest contribution from El Niño usually occurs in the year after the peak in El Niño, not in the year when the warm ocean temperatures in the tropical Pacific Ocean associated with El Niño are increasing. Hence, due to the current El Niño, it is likely that 2016 will set a new record high global teSmperature, even hotter than in 2015.

"Further analysis available at climatecentral.org"

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Prof Sir Brian Hoskins, Chair of the Grantham Institute at Imperial College London, comments:

“Carbon dioxide in the atmosphere is at record levels and so are global temperatures. These are indicators of the big climate problem we are creating for ourselves, and set the tone of great urgency for the negotiators in Paris to make a meaningful agreement that will put us on the road of greenhouse gas emission reductions and elimination that will limit climate change to an amount that we can probably cope with.”