Tuesday, September 04, 2012

And now for the weather report

Perhaps a few more weather reporters giving this kind of context could help public understanding, since studies indicate that weather reporters remain one of the primary sources of information about climate (despite many reporters having little or background in climate themselves).

Very helpfully, the American Meteorological Society has updated its statement on climate change to reflect scientific research completed since the last one in 2007. The new statement is considerably stronger in its language than its previous one. Here are a few tastes of the new statement:

"Warming of the climate system now is unequivocal [...] many of the observed changes noted above are beyond what can be explained by the natural variability of the climate. It is clear from extensive scientific evidence that the dominant cause of the rapid change in climate of the past half century is human-induced increases in the amount of atmospheric greenhouse gases [...] Since long-term measurements began in the 1950s, the atmospheric CO2 concentration has been increasing at a rate much faster than at any time in the last 800,000 years. [...] Climate is potentially predictable for much longer time scales than weather for several reasons. [...] A helpful analogy in this regard is that population averages of human mortality are predictable while life spans of individuals are not. [...] Future warming of the climate is inevitable for many years due to the greenhouse gases already added to the atmosphere and the heat that has been taken up by the oceans. [...] Global efforts to slow greenhouse gas emissions have been unsuccessful so far. However, were future technologies and policies able to achieve a rapid reduction of greenhouse gas emissions — an approach termed “mitigation” — this would greatly lessen future global warming and its impacts. [...] In the 21st century, global sea level also will continue to rise although the rise will not be uniform at all locations. [...] Atmospheric water content will increase globally, consistent with warmer temperatures, and consequently the global hydrological cycle will continue to accelerate. [...] changes in precipitation patterns are expected to differ considerably by region and by season [...] more severe droughts and floods [...] significant regional shifts in precipitation patterns [...] heavy precipitation events will continue to become more intense and frequent [...] longer dry spells between precipitation events in the subtropics and lower-middle latitudes [...] Widespread retreat of mountain glaciers is expected to eventually lead to reduced dry season flows for glacier-fed rivers. Drought is projected to increase over Africa, Europe, and much of the North American continental interior, and particularly the southwest United States. [...] more extreme warm periods and fewer cold periods are expected [...] more severe episodes of extreme heat. Critical thresholds of daily maximum temperature, above which ecosystems and crop systems (e.g., food crops such as rice, corn, and wheat) suffer increasingly severe damage, are likely to be exceeded more frequently. [...] It is unclear if the land biosphere and oceans will be able to continue taking up carbon at their current rate into the future. [...] Another unknown is the amount of methane that will be released due to high-latitude warming. There are indications that large regions of the permafrost in parts of Alaska and other northern polar areas are already thawing, with the potential to release massive amounts of carbon into the atmosphere beyond those being directly added by human activity. The portion of the increased CO2 release that is absorbed by the world ocean is making the ocean more acidic, with negative implications for shell- and skeleton-forming organisms and more generally for ocean ecosystems."
If you're pressed for time, or already familiar with recent climate research, then you can just skip to the conclusion. Here it is in full:
"There is unequivocal evidence that Earth’s lower atmosphere, ocean, and land surface are warming; sea level is rising; and snow cover, mountain glaciers, and Arctic sea ice are shrinking. The dominant cause of the warming since the 1950s is human activities. This scientific finding is based on a large and persuasive body of research. The observed warming will be irreversible for many years into the future, and even larger temperature increases will occur as greenhouse gases continue to accumulate in the atmosphere. Avoiding this future warming will require a large and rapid reduction in global greenhouse gas emissions. The ongoing warming will increase risks and stresses to human societies, economies, ecosystems, and wildlife through the 21st century and beyond, making it imperative that society respond to a changing climate. To inform decisions on adaptation and mitigation, it is critical that we improve our understanding of the global climate system and our ability to project future climate through continued and improved monitoring and research. This is especially true for smaller (seasonal and regional) scales and weather and climate extremes, and for important hydroclimatic variables such as precipitation and water availability.

Technological, economic, and policy choices in the near future will determine the extent of future impacts of climate change. Science-based decisions are seldom made in a context of absolute certainty. National and international policy discussions should include consideration of the best ways to both adapt to and mitigate climate change. Mitigation will reduce the amount of future climate change and the risk of impacts that are potentially large and dangerous. At the same time, some continued climate change is inevitable, and policy responses should include adaptation to climate change. Prudence dictates extreme care in accounting for our relationship with the only planet known to be capable of sustaining human life."
There is much to commend in this new statement. It clearly and unambiguously affirms the three basic pillars of climate science: (a) the planet is warming rapidly; (b) humans are the dominant cause; (c) the consequences are a serious threat. There is not a relevant scientific institution of national or international standing that questions any of those three claims.

At the same time, the new AMS statement acknowledges many areas of lower confidence, where research is ongoing, including: the precise sensitivity of the climate to greenhouse gases; the precise role of clouds and aerosol particles; the precise distribution of disruptions to the hydrological cycle; the ongoing effects of natural variation within the larger trends; the rate of ice sheet disintegration and sea level melt; the potential negative side effects of geo-engineering proposals; and perhaps most importantly the uncertainties in the human systems that cause and are impacted by climate change: how fast will we continue to modify the chemical composition of atmosphere and oceans? And how well will we respond to the risks and threats these changes will bring?

Given the uncertainties, both in the geophysical systems and especially in the human systems that drive and respond to them, the AMS statement remains agnostic about the most important debate regarding the threat of climate change: does climate change represent a level of risk that is merely disastrous or truly catastrophic?

The closest it comes to addressing this question is in the very interesting final sentence: "Prudence dictates extreme care in accounting for our relationship with the only planet known to be capable of sustaining human life." We're not talking merely about losing the polar bears, or an acceleration of species extinctions more generally, or even severe economic disruption or a rising threat of climate-related conflict. Implicitly at least, this statement acknowledges that what is at stake is the ongoing capacity of the planet to sustain human life.

UPDATE: The scriptwriter for the video above shares his thinking behind the clip.


byron smith said...

"2º[C], which is universally accepted as the threshold of total mayhem."
This was probably the most misleading part of the video (which was intended as humour, well, perhaps black humour).

(a) Climate impacts are not so neat as to fit clearly into <2ºC = safe and >2ºC = total mayhem. They just get worse and worse the higher you go. International negotiations have focussed on 2ºC for the last ten years or so, though this has had more to do with convenience and picking an easily communicated number than anything inherent in 2ºC itself.

(b) Likely impacts at 2ºC are now considered to be considerably worse than they were thought to be ten or even five years ago, meaning that 2ºC cannot by any means be considered "safe".

(c) "Total mayhem" does not suddenly appear at 2ºC. Basically, negative impacts get worse and worse the higher we go (and the few positive impacts basically disappear once you go much above 1-1.5ºC).

(d) Or chances of keeping warming below 2ºC are now close to zero, barring a sudden collapse of industrial civilisation. Perhaps a global war-scale mobilisation combined with a bit of luck over sensitivity and some timely technical breakthroughs could do it, but that's making a whole iceberg of fairly unlikely assumptions and needing them to all be true simultaneous.

So I'd rather use 2ºC as a educational tool to highlight just how bad things will still be even on the most optimistic pathway than as a line between safety and mayhem.

byron smith said...

A collection of recent extreme weather events can be found here.