Aggressive action on climate change is non-negotiable

By Hoesung Lee 15 December 2015

According to the World Meteorological Organization, 14 of the 15 hottest years on record have occurred in this century. Photo by: Abt Associates

As negotiators from 195 countries gather in Paris this month to hammer out a global agreement to limit climate change, their discussion will be guided in part by the findings of the Intergovernmental Panel on Climate Change. Those findings are contained in the IPCC’s fifth Assessment Report, or AR5, a comprehensive, rigorously assembled document that provides in-depth information not only about climate science but the options for adapting to and preventing climate change.

Notwithstanding the attention given to AR5 when it was released beginning in September 2013, I frequently hear claims that are not supported by AR5. So, on the verge of the historic negotiations in Paris, I would like to take this opportunity to respond to some of the more frequent misconceptions about climate change.

Global temperatures are continuing to increase. Data from AR5’s Working Group I showed that average global temperatures appeared to have temporarily leveled off after an unusual peak in 1997. (I say “appeared” because more recent statistical analyses not included in AR5 indicate that there was no level-off.) This, in turn, has been cited as an acknowledgement by the IPCC that warming is no longer increasing. But that is not what the IPCC conveyed.

The IPCC has been very clear that temperatures are still trending higher and that we should not be misled by short-term fluctuations. To quote from Working Group I: “Although each year and even decade is not always warmer than the last, global surface temperatures have warmed substantially since 1900.”

This statement is amply borne out the following graph from the World Meteorological Organization.  (I show it here because it includes data points that were gathered after the completion of AR5.) There are pullbacks, to be sure, but the trend toward higher temperatures is unmistakable.

Source: World Meteorological Organization: World Climate Data and Monitoring Program

Working Group I concluded that temperatures would continue their upward trajectory with the additional emission of heat-trapping gases in the atmosphere.

The recent temperature record is proving that point. As the WMO noted earlier this year, 14 of the 15 hottest years on record have occurred in this century. Of those years, 2014 was the hottest, and 2015 is set to be still hotter.

The Earth continues to warm.

Recent temperature increases are not part of normal variation. Natural factors — from volcanic eruptions and the sun’s intensity to fluctuations in the El Niño-Southern Oscil­lation — do indeed cause global temperatures to fluctuate. But none of them explain the rapid rise in temperatures since the dawn of the Industrial Revolution. The only thing that explains them is the build up of heat-trapping gases in our atmosphere from human activities.

A few excerpts from Working Group I illustrate that we have entered a period unlike any in human history and which cannot be explained by natural variability.

● Warming of the climate system is unequivocal, and since the 1950s, many of the observed changes are unprecedented over decades to millennia.

● The rate of sea level rise since the mid-19th century has been larger than the mean rate during the previous two millennia.

● The atmospheric concentrations of carbon dioxide, methane and nitrous oxide (gases that cause climate change) have increased to levels unprecedented in at least the last 800,000 years.

The evidence clearly shows that human activity is the driver of our warming climate. Our influence has been detected in not only the warming of the atmosphere but in sea level rise, the global water cycle, reductions in snow and ice, and changes in some weather extremes.

That’s why AR5 concluded that it is extremely likely (95 percent confidence) that human

Influence has been the dominant cause of the observed warming since the mid-20th century.

The cost of preventing climate change is affordable. I often hear dire predictions that the massive shift to a carbon-free economy will be ruinous to the global economy. The IPCC’s Working Group III, which assessed options for preventing climate change, acknowledged that preventing additional climate change would not be easy. It will require changes throughout the global economy including a shift in investment away from fossil fuels and toward greater energy efficiency, renewable energy and carbon capture technology.

But, based on a wide range of economic forecasts, such a shift is affordable. In fact, given the peril of doing nothing, we can’t afford not to take action. Economists forecast global consumption to increase an average of 2.8 percent per year this century. Aggressive mitigation would be expected to shave about 0.06 percentage points off that annual figure.

The lowered consumption figure becomes even more affordable when you consider that it does not include the numerous benefits of preventing climate change, such as improved health, employment gains, a more secure and resilient energy supply, and water and food security.

Indeed, a low-carbon world in which the climate is stabilized will present many new economic and employment opportunities.

With the effects of climate change already emerging on every continent, the window of opportunity to take action is narrowing. And the longer we delay mitigation the more we increase the difficulty and narrow the options for limiting the increase in warming to 2 degrees Celsius or less since pre-industrial times.

That’s why I am hopeful that the negotiations in Paris will set the world on a path to sharply reducing — and ultimately eliminating — our greenhouse gas emissions. The alternative of severe, persistent and irreversible impacts is unthinkable.

Planet Worth is a global conversation in partnership with Abt Associates, Chemonics, Helvetas, Tetra Tech, the U.N. Development Programme and Zurich, exploring leading solutions in the fight against climate change, while highlighting the champions of climate adaptation amid emerging global challenges. Visit the campaign site and join the conversation using #PlanetWorth.

About the author

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Hoesung Lee

Hoesung Lee is a professor in economics of climate change, energy and sustainable development at Korea University’s Graduate School of Energy and Environment in the Republic of Korea. He serves on various boards including as executive member of the Korean Academy of Environmental Sciences; a member of the Asia Development Bank President’s advisory board, a council member of the Global Green Growth Institute and an editorial board member of UK based Climate Policy.


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