There is no question that Earth's surface temperature has ramped up in the last 150 years. The oceans themselves are experiencing heat waves and in April, Pakistan recorded the highest temperature ever measured anywhere for that month: 50.2 degrees Celsius (122.36 Fahrenheit).
In those 150 years, there were three periods when the warming halted or at least slowed. The causes were natural, claims a new paper published in Science Advances on Wednesday. The chief effects in the most recent slowdown that ended in 2013 were short-term solar cycles and ocean temperature patterns and volcanic activity.
In other words, the perpetual eruption by Hawaii's Kilauea since 1983 and the explosion of Fuego in Guatemala, to name but two major volcanic events, are locally distressing but are helpful on the planetary scale, albeit briefly.
Yes, volcanic eruptions and their associated ash clouds helped deflect sunlight and slow global warming not by much but by a statistically significant degree a little, say Chris Folland of the Meteorological Office Hadley Center and colleagues.
"If we have volcanic cooling, it does buy us a little bit of time. So does extra solar cooling," Folland told Haaretz. "It buys us a little bit of extra time to respond through mitigation or adaptation to global warming."
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Note that there have been no eruptions on a global scale in this time, just local ones. "I drew attention to [volcanism] because it shows up as small, but significant, due to an increase in volcanic activity in many parts of the world. There were no big players here, but there were enough to cause a small cooling effect."
So we can either throw ourselves at the clay feet of our political leaders and hope they're talking the truth about actually doing something about climate change, or pray for more volcanoes. Up to you.
Don't let the sunshine in
Meanwhile, taking data starting in 1891, Folland and the team used statistical methods to analyze what part of the warming/cooling trends could be explained by natural causes. Further climate developments beyond what nature could explain has to be anthropogenic - caused by human activities.
The team supports the absolute majority of scientists in blaming humans for most of the warming over these 150 years, though obviously the relative contributions of the various factors differed over time.
The question is what caused warming to slow during three periods (1896 to 1910, 1941 to 1975, and 1998 to 2013). The team's conclusion is that the causes were natural.
The first of the three downturns began in 1891, and lasted to 1910. Folland stresses that the data about this period (the only one of definite cooling) is partial and conclusions should therefore be taken with caution. That caveat noted, the team thinks a key cause of decrease in global mean surface temperature this first time was the El Nino-El Nina weather patterns.
Regarding the second slowdown, from the start of World War II to 1975, science is still arguing whether that involved actual cooling or not, Folland observes. He notes that if we start at 1941, there is a small cooling, but "if we take out World War II to 1944, we have pretty much no change over the following period to 1975," he says. Again there could be missing data issues. Anyway, increased volcanism was a factor in the second slowdown, the team deduces.
The most recent downturn in warming was from 1998 to 2013 – "that one is known as the Pause," Folland observes. This hiatus has been grist to the mill of climate change deniers, not least U.S. President Donald Trump.
"The third slowdown is the one that caused all the controversy," Folland says. Did it happen? Didn't it? It did, the team has proven.
"Our main conclusion in the last five years was that there was a slowdown, but not an actual stop in warming. A key cause was an increase in the frequency of the la Nina events in the Pacific and also a volcanic component," Folland says.
A new element the paper presents is the contribution of the sun's behavior. The team checked month by month and demonstrated that a major component of that slowdown from 2001 to 2010 was a larger than usual reduction in solar output. "We claim there is a solar signal in the cooling," Folland sums up.
The 11-year solar cycle kicked off the third slowdown in warming, Folland says, because it was unusually protracted and the decrease in solar output was much greater than normal. Now solar output is maximal again.
All this said, neither the sun's cycles nor Nino-Nina weather patterns are a function in the global warming trend. They come, they go. They can be predicted but their intensity cannot be forecasted. Volcanoes exploding all over the place might help give us time, up to a point.
One last point. The paper demonstrates another crucial thing. Be not loud, Donald: they proved that continuing greenhouse gas emissions managed to offset the cooling effects of aerosols (particles of gunk in the air from power stations and the like, which reflect solar radiation back into outer space.) Naturally, the first cooling period, before WWI, there weren't many emissions; there were substantially more in the second period and now there are a lot more. The point is that the background warming continues unchecked.