August 31, 2020

Not Your Grandparents’ Climate

An Occasional Commentary on Current Climate Related Developments


Extreme Heat, Awe Inspiring Lightning and Destructive Wildfires

Many, if not most, of the most destructive wildfires in recent years in California have been ignited by failures of the electrical grid. This week’s events have served as a vivid reminder, though, that we can’t forget that wildfires can also be started by natural events. Since late last week, California has been experiencing a record breaking heat wave (see Daniel Swain’s blog for the detailed meteorology: that has resulted in rolling power blackouts across the state as air conditioning use has skyrocketed. The warm air also mixed with the remnants of Pacific Hurricane Elida, producing an awe inspiring display of thunder and lightning Saturday night in the Bay Area that ignited major wildfires across the region ( that have caused air quality indices to rapidly rise to unhealthy levels.

We can expect to see more frequent and intense heat waves in California as temperatures continue to rise. As that will also lead to increasing moisture in the atmosphere, historically rare summer convective rain events such as the one we have just experienced, accompanied by the threat of widespread wildfire ignition, may well also become more common. Both highlight the need for a sense of urgency in controlling carbon emissions and finding ways to remove carbon already in the atmosphere. Unfortunately, even the most valiant efforts on both of these fronts won’t spare us from the decades of worsening climatic conditions that lie ahead of us, so it is also imperative that we have a sense of urgency about preparing for them. In California, as in many other places, wildfires are responsible for lost lives, damaged ecosystems, destruction of property and widespread health impacts due to smoke, representing one of our greatest climate threats. While we can’t prevent higher temperatures in the near term, we can take steps to lower the risk of wildfires. Hardening the electrical grid to reduce ignition risks without disruptive, and potentially lethal, preemptive power outages is one obvious measure that will make a huge difference. However, as we’ve just seen, there are other sources of ignition we also can’t ignore and can’t eliminate. The only way to mitigate that threat is to reform our management practices for forests and wildlands to make them more resilient to wildfires, something that has been urged by experts for years: fire and forest management.

And, In Case You Haven’t Noticed, Summers Have Gotten Hotter!

Dan Miller of the Roda Group recently brought to my attention the following pair of Northern Hemisphere summer temperature distributions showing the significant difference between 1951-1980 and 2009-2019, which he discussed in a blog he published in July: Extremely Hot Summers Now Happen 200X More Often Than 50 Years Ago.

Created by James Hansen, they show how the distribution of temperature values are distributed by the number of standard deviations from the 1951-1980 mean. James Hansen, of course, formerly director of the NASA Goddard Institute and currently director of the Program on Climate Science, Awareness and Solutions at Columbia University’s Earth Institute, was one of the first scientists to recognize the threat of global warming and testified about it to Congress in 1988. Since then, he has been a tireless advocate for strong climate action. As Dan points out in his blog, a key takeaway from these curves is that extremely hot summers, defined as more than 3 standard deviations above the 1951-1980 mean, are 200 times as frequent as they were then. You can also see that the most frequent temperature is now about 1.5 standard deviations higher than it was then and that the upper tail of the current distribution has grown fatter, meaning that temperature extremes have become more common.

Dan and Hansen have also worked together to promote action on climate mitigation, including coauthoring a paper last year outlining why a fee and dividend carbon tax is the most effective carbon pricing policy in terms of reducing emissions: fee and dividend.


Local Warming But Far Reaching Consequences

As mean global temperatures have increased, they have not done so equally everywhere. It’s well known that the Arctic is warming twice as fast as the Earth as a whole but there are also other hot spots at lower latitudes. Recently, The Washington Post published an analysis of temperature increases in the contiguous US, that highlighted such a hot spot in Colorado on the western slope of the Rockies that stretches into neighboring Utah: Colorado hot spot. Temperatures there have risen by 2-3 deg C since 1895, more than double the overall warming of the Earth of about 1 degree C since the Industrial Revolution. While the local impacts are severe, the implications are far broader since with the declining snowpack in the Rockies and more rapid evaporation due to higher temperatures, flows in the Colorado River, an important source of water for the Colorado River Basin States–Wyoming, Colorado, Utah, New Mexico, California, Arizona and Nevada–have also been adversely affected. As with rapid Arctic warming, which many scientists believe has led to more frequent and severe midlatitude extreme events, this is a reminder that localized climate impacts can have far reaching consequences as the result of such things as physical connections, economic links and migration patterns, something that those planning climate adaptation measures need to keep firmly in mind.


The Future Climate May be More Predictable Than We Thought

One of the most challenging aspects of climate change is that experience and historical data are rapidly becoming less and less reliable guides to what we should do. And, while models of the future climate have been steadily improving, they are still not not where we need them to be in terms of spatial resolution and a robust representation of conditions at local, or even regional scales. According to NCAR Distinguished Scholar Kevin Trenberth, one of their major limitations is their inability to accurately reproduce major climate modes such as the El Nino-Southern Oscillation (ENSO), the Pacific Decadal Oscillation (PDO), the Madden-Julian Oscillation (MJO) and the North Atlantic Oscillation (NAO), which are all major contributors to the natural variability of the climate (private communication). One example of current model limitations is modeling the behavior of clouds, whose physics are still not fully understood. In addition, because clouds are much smaller than global climate model grid cells, they have to be represented by heuristic approximations known as parameterizations rather than by physical models of their behavior. Since future climatic conditions are a combination of natural variability and the climate change signal, the inability to faithfully reproduce natural variability means climate model projections are less reliable than they could be, especially at local and regional scales that are critical to formulating effective adaptation strategies.

Underscoring this point, a recent paper in Nature by Smith et al has found that it is possible to extract reliable retrospective predictions of the NAO from a CMIP5 multimodel ensemble of simulations, although the individual models underestimate that signal by a factor of 200: NAO more predictable than models imply. According to the authors, while current climate models are in good agreement on large scale temperature changes, this is not the case for atmospheric circulation patterns. They conclude that as a result, regional projections, especially for precipitation, are low confidence. This may sound discouraging after all of the work that has gone into developing and improving global climate models, but it also identifies an opportunity for a major step forward. If some of the considerable talent in modeling centers around the world can be applied to making progress on reducing this weakness in current models, future models will be that much more skillful, and useful!

Article By:

Robert Dickinson


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