Sun sets on climate change get-out clause

Potsdam Institute of Climate Research’s Georg Feulner

Reduced heating from the Sun will not rescue Earth from global warming, according to Potsdam Institute for Climate Research’s Georg Feulner. “Many people believing in a strong Sun-climate connection suggested that this could save us,” he says. “This claim is not supported.”

Feulner and his colleague Stefan Rahmstorf have produced computer models simulating what would happen if the Sun entered an extended quiet period known as a “grand minimum”. The energy falling on the Earth from the sun normally varies between highs and lows over eleven year cycles. However, the cycle can get stuck at a low for decades, and with the current cycle’s low period already being unusually long, there has been speculation that we’re entering another grand minimum. “Four such minima have occurred during the last millennium, so a new grand minimum in the 21st century is entirely possible,” Feulner explains.

The German scientists looked at what would happen if a grand minimum like the one thought to be responsible for a “Little Ice Age” between 1645-1715 was repeated. They found that if carbon emissions continue as they are, a grand minimum would reduce the 3.7°C rise from 1990 temperatures predicted by 2100 by just 0.3°C at most. However, as you can see in the graph below, recent years have not warmed as much as this model might suggest, so I asked Feulner why this was.

“While most climate models can adequately reproduce observed global temperatures, some elements of natural climate variability are still difficult to model,” the scientist answers. “For climate change, however, all that matters is the long-term trend, and if you look at the past rise of temperatures, similar periods of ‘flat’ temperatures have occurred in the past, superimposed on a trend of rising temperatures. So the current stagnation of global temperatures is statistically not really that surprising.” He notes that as well as a quiet sun, before this winter there were years where “La-Niña” was seen in the Pacific, which is also linked with lower global temperatures.

Feulner and Rahmstorf’s projections for the impact of lower solar activity on global warming are shown in dashed lines, with the solid lines representing normal 11-year cycles. Credit: Potsdam Institute for Climate Impact Research

The purpose of this blog is to try and pull together an accurate and simple explanation of climate change. Having created his own simulations of the world’s climate, Feulner is one of the best qualified scientists I’ve spoken with to do this, so I asked him to help.

“Every day humans burn large amounts of fossil fuels like coal, gas and oil to produce energy and goods,” he says. “These fossil fuels contain carbon atoms which are converted to carbon dioxide (CO2) during combustion. This CO2 is released to the atmosphere where it acts as a ‘greenhouse’ gas: CO2 traps outgoing radiation and leads to a warming of the atmosphere.”

“Since the beginning of the industrialisation, measurements show that CO2 concentrations in the atmosphere have increased by about a third, and global temperatures have been recorded to have increased by about 0.8 degrees. If CO2 emissions continue to rise as in the past, temperatures could be several degrees higher in the year 2100, which would result in predominantly negative impacts on the environment and human societies. We know how much fossil fuel we burn and these rates are in agreement with the measured rise in atmospheric CO2 concentrations, once ocean uptake is considered. And we know the greenhouse-gas effect of CO2, so an increasing CO2 concentration will yield to global warming as observed.”

This, one of the simplest, most direct explanations of climate change on Simple Climate so far, emphasises Feulner’s expertise in his field. Yet despite this, and his success in addressing questions about the Sun’s impact on climate change, Feulner would rather the outlook was different. “Most climate scientists wish they could be wrong, but the evidence is already overwhelming – and still accumulating,” Feulner admits. “I am still overwhelmed that humans have so fundamentally changed the Earth in terms of landscape, biodiversity and climate.”