Global temperatures cross one-degree warming threshold

The 1 °C threshold is an important marker, representing the midway point to the 2 °C limit that most agree the planet needs to stay within to mitigate the worst effects of climate change. Based on data from January to September, the results show a global mean temperature at 1.02 °C above the 1850-1900 reference period.   

“This year marks an important first but that doesn’t necessarily mean that every year from now on will be a degree or more above pre-industrial levels, as natural variability will still play a role in determining the temperature in any given year,” said Peter Stott, head of Climate Monitoring and Attribution at the Met Office’s Hadley Centre for Climate Prediction and Research.

Natural variability for 2015 has included the effects of El Nino, the sporadic Pacific weather system that generally has a warming effect on the Earth’s temperature. But according to the Met Office, similar events in the past have never been enough to push global temperatures across the 1 degree threshold.

“We have seen a strong El Nino develop in the Tropical Pacific this year and that will have had some impact on this year’s global temperature,” said Stephen Belcher, director of the Met Office’s Hadley Centre.

“We’ve had similar natural events in the past, yet this is the first time we’re set to reach the 1 °C marker and it’s clear that it is human influence driving our modern climate into uncharted territory.”

The announcement comes at an important time, with the Paris climate talks set to get under way later this month. Although we are halfway to 2 °C of warming, the Met Office says we have already used up more than two-thirds of the carbon budget (2,000 GtCO₂ out of an estimated budget of 2,900 GtCO₂) that would keep us under that marker. This is due to the delayed warming effects of CO₂ as it remains in the atmosphere for many years after it is emitted.

According to Myles Allen, a Professor of Geosystem Science at the University of Oxford, governments should be framing emissions reduction against future warming rather than targeted dates in the future. He said that when considering the actions required to stay within 2 °C, there is a simple way of thinking about the problem.

“Once we reach one degree, then we need to reduce emissions by 10 per cent of baseline for every tenth of a degree warming thereafter if we are to meet the two degree goal,” Allen explained.

“That’s a really simple way of thinking about it. We think it would be really helpful if governments were to think about it in this way, framing their objectives against future warming rather than against arbitrary dates, because it links progress trajectory to the target they have set themselves.