Understanding Climate Change – No Simple Answers

One example cited in an insightful essay on climate change published by the Economist is the fact that over the past 15 years air temperatures at the Earth’s surface have been flat while greenhouse-gas emissions have continued to soar.

According to the article, the world added roughly 100 billion tonnes of carbon to the atmosphere between 2000 and 2010 – about a quarter of all the CO₂ put there by humanity since 1750, but as James Hansen, the soon to retire head of NASA’s Goddard Institute for Space Studies, observes, “the five-year mean global temperature has been flat for a decade.”

By no means does this indicate that global warming is a delusion, notes the Economist. Temperatures in the first decade of the 21st century are almost 1°C above those of the first decade of the 20th. But it does mean that our models may not be accurate enough to pinpoint the pace and severity of global warming impacts.

A recent doctoral thesis from the University of Gothenburg, Sweden tested a variety of climate models and found only a few were able to reproduce the observed changes in extreme precipitation in China over the past 50 years.

At the core of most climate models is the measurement of climate reactions to changes in carbon-dioxide levels – “climate sensitivity” usually defined as how much hotter the Earth will get for each doubling of CO₂  concentration levels.

After taking into account a host of systemic interactions and feedback loops, climate scientists seek to estimate the probable level of average temperature rise over time and the thresholds beyond which life as we know it will be forever changed – usually pegged at above 4°C.

Notes the Economist, the Intergovernmental Panel on Climate Change (IPCC), which embodies the mainstream of climate science, reckons the answer is about 3°C, plus or minus a degree or so, though a higher range could be part of the next IPCC report due in September.

But a host of new studies suggest that the actual rate of temperature change associated with a doubling of CO₂ levels may be quite lower – in the 2.3°C range or lower, which suggests the chances of climate sensitivity rising above 4.5°C, becomes “vanishingly small”.

The significance of this change in estimates goes far beyond the need to revise the science of climate change. The impact on corporate and public policies focused on mitigation measures associated with global warming and rising greenhouse gases could be staggering.

Leaving aside all of the conspiracy theory arguments for or against the science of climate change, the simple fact remains that our climate models still cannot account for all the observable phenomena of changing weather patterns or the localized climatic influences and feedback loops that amplify or sometimes moderate climate change.

A different metric

While the climate sensitivity models have been the benchmark in climate science their ability to predict what could happen to our climate once all the puts and tales and feedback mechanisms have been taken into consideration is proving to be too long for most policymakers – centuries in fact.

A more useful metric from a policy viewpoint could be the transient climate response (TCR), the temperature you reach after doubling CO₂ gradually over 70 years. Notes the Economist, “Unlike the equilibrium response, the transient one can be observed directly; there is much less controversy about it.”

Most estimates put the TCR at about 1.5°C, with a range of 1-2°C. Notes the article:

“As a rule of thumb, global temperatures rise by about 1.5°C for each trillion tonnes of carbon put into the atmosphere. The world has pumped out half a trillion tonnes of carbon since 1750, and temperatures have risen by 0.8°C. At current rates, the next half-trillion tonnes will be emitted by 2045; the one after that before 2080.”

Taking everything into consideration, this would suggest an increase in temperatures compared with pre-industrial levels of around 2°C with levels of 4°C at the far top end of the estimates.

While this may sound more reassuring compared to those who suggest a 4°C rise is imminent and beyond that lays the total collapse of the Earth’s capacity to sustain life as we know it, from the point of view of corporate planners and policy makers little has changed.

As noted by the Economist despite all the work on sensitivity analysis, no one really knows how the climate would react if the Earth’s temperatures rose by as much as 4°C.

Observable real world changes in weather patterns, sea level rises, droughts, disruptions in agricultural and biodiversity patterns, etc., are real issues that must be acted on today, regardless of whether the global temperature rises to anywhere near 4°C in 70 years or longer.

All the imperatives for more sustainable infrastructure planning, climate mitigation planning, and more efficient use of lower carbon energy remain.

In time, climate science will catch up to climate realities. But today’s policy makers and business planners must deal with the realities of the next three decades as best they can determine. Let’s hope they get it right.

The Economist article is available here

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