Climate models have accurately predicted global heating, study finds | Environment | The Guardian

Climate models have accurately predicted global heating, study finds | Environment | The Guardian

Findings confirm reliability of projections of temperature changes over last 50 years

Climate models have accurately predicted global heating for the past 50 years, a study has found.

The findings confirm that since as early as 1970, climate scientists have had a solid fundamental understanding of the Earth’s climate system and the ability to project how it will respond to continued increases in the greenhouse effect. Since climate models have accurately anticipated global temperature changes so far, we can expect projections of future warming to be reliable as well.

The research examines the accuracy of 17 models published over the past five decades, beginning with a 1970 study and including 1981 and 1988 models led by James Hansen, the former Nasa climatologist who testified to the US Senate in 1988 about the impacts of anthropogenic global heating. The study also includes the first four reports by the UN’s intergovernmental panel on climate change (IPCC).

“We found that climate models – even those published back in the 1970s – did remarkably well, with 14 out of the 17 model projections indistinguishable from what actually occurred,” said Zeke Hausfather, of the University of California, Berkeley, and lead author of the paper.

Timeline

Half a century of dither and denial – a climate crisis timeline

Fossil fuel companies have been aware of their impact on the planet since at least the 1950s

The physicist Edward Teller tells the American Petroleum Institute (API) a 10% increase in CO2 will be sufficient to melt the icecap and submerge New York. “I think that this chemical contamination is more serious than most people tend to believe.”

Lyndon Johnson’s President’s Science Advisory Committee states that “pollutants have altered on a global scale the carbon dioxide content of the air”, with effects that “could be deleterious from the point of view of human beings”. Summarising the findings, the head of the API warned the industry: “Time is running out.”

Shell and BP begin funding scientific research in Britain this decade to examine climate impacts from greenhouse gases.

A recently filed lawsuit claims Exxon scientists told management in 1977 there was an “overwhelming” consensus that fossil fuels were responsible for atmospheric carbon dioxide increases.

An internal Exxon memo warns “it is distinctly possible” that CO2 emissions from the company’s 50-year plan “will later produce effects which will indeed be catastrophic (at least for a substantial fraction of the Earth’s population)”.

The Nasa scientist James Hansen testifies to the US Senate that “the greenhouse effect has been detected, and it is changing our climate now”. In the US presidential campaign, George Bush Sr says: “Those who think we are powerless to do anything about the greenhouse effect forget about the White House effect … As president, I intend to do something about it.”

confidential report prepared for Shell’s environmental conservation committee finds CO2 could raise temperatures by 1C to 2C over the next 40 years with changes that may be “the greatest in recorded history”. It urges rapid action by the energy industry. “By the time the global warming becomes detectable it could be too late to take effective countermeasures to reduce the effects or even stabilise the situation,” it states.

Exxon, Shell, BP and other fossil fuel companies establish the Global Climate Coalition (GCC), a lobbying group that challenges the science on global warming and delays action to reduce emissions.

Exxon funds two researchers, Dr Fred Seitz and Dr Fred Singer, who dispute the mainstream consensus on climate science. Seitz and Singer were previously paid by the tobacco industry and questioned the hazards of smoking. Singer, who has denied being on the payroll of the tobacco or energy industry, has said his financial relationships do not influence his research.

Shell’s public information film Climate of Concern acknowledges there is a “possibility of change faster than at any time since the end of the ice age, change too fast, perhaps, for life to adapt without severe dislocation”.

At the Rio Earth summit, countries sign up to the world’s first international agreement to stabilise greenhouse gases and prevent dangerous manmade interference with the climate system. This establishes the UN framework convention on climate change. Bush Sr says: “The US fully intends to be the pre-eminent world leader in protecting the global environment.”

Two month’s before the Kyoto climate conference, Mobil (later merged with Exxon) takes out an ad in The New York Times titled Reset the Alarm, which says: “Let’s face it: the science of climate change is too uncertain to mandate a plan of action that could plunge economies into turmoil.”

The US refuses to ratify the Kyoto protocol after intense opposition from oil companies and the GCC.

The US senator Jim Inhofe, whose main donors are in the oil and gas industry, leads the “Climategate” misinformation attack on scientists on the opening day of the crucial UN climate conference in Copenhagen, which ends in disarray.

A study by Richard Heede, published in the journal Climatic Change, reveals 90 companies are responsible for producing two-thirds of the carbon that has entered the atmosphere since the start of the industrial age in the mid-18th century.

The API removes a claim on its website that the human contribution to climate change is “uncertain”, after an outcry.

Mohammed Barkindo, secretary general of Opec, which represents Saudi Arabia, Kuwait, Algeria, Iran and several other oil states, says climate campaigners are the biggest threat to the industry and claims they are misleading the public with unscientific warnings about global warming.

Jonathan WattsGarry Blight and Pablo Gutiérrez

Based on modern climate model projections, if countries follow through with current and pledged climate policies, the world is on track for about 3C of warming above pre-industrial temperatures by 2100 – a situation the IPCC and others predict would be catastrophic.

The challenge in evaluating climate model accuracy lies in the fact that due to computing power limitations, simulations are only run for a few specific future greenhouse gas emissions scenarios. There are an infinite number of such possible scenarios, but real-world emissions will follow only one path, and it will never exactly match the few scenarios input into climate models. Thus, if Earth warms less than in a climate model projection, it does not necessarily mean the model was inaccurate.

Put simply, climate scientists are not in the business of predicting human fossil fuel consumption but are attempting to accurately simulate how the climate will change in response to a given rise in greenhouse gas emissions.

“Future emissions depend on human behaviour, not physical systems, and climate models should be evaluated on their physics rather than the future emission projections,” said Hausfather.

In nearly half of the model projections examined in the paper, the input scenarios were significantly different from the real-world changes in greenhouse gas emissions. As a result, projected temperature changes were only consistent with observed global warming in 10 of the 17 models, with four projecting more warming and three projecting less than subsequently occurred.

However, the study authors addressed these inconsistencies by evaluating the change in temperature per change in “radiative forcing” – the global energy imbalance caused by the increased greenhouse effect and other factors – in models against what happened in the real world. This metric reveals whether the climate models are accurately producing the temperature response to a given emissions change – in essence, whether are accurately simulating the physical response of Earth’s climate system. With this factored in, 14 of the 17 models were accurate.

“The rate of warming we are experiencing today is pretty much exactly what past climate models projected it would be,” said Hausfather.

Those who oppose policies to limit the impacts of global heating have long sought to undermine the credibility of climate models. If the model projections are considered unreliable, they argue, then we do not know how urgent slowing global warming is. As a result, “climate models are unreliable” has become a popular myth propagated by climate deniers.

The latest study adds to the body of evidence supporting the accuracy of climate models, and will be welcomed by those arguing that more aggressive climate policies are needed to avoid dangerous levels of global warming. The UN climate summit in Glasgow in 2020 will be crucial, as countries will be expected to commit to scaling up the emission reductions that were pledged in the 2015 Paris agreement on climate change.

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