22 march 2009

An introduction to global warming impacts: Hell and High Water

Joseph Romm, Climate Progress, March 22, 2009

In this post, I will examine the key impacts we face by 2100 if we stay anywhere near our current emissions path. I will focus primarily on:

•Staggeringly high temperature rise, especially over land — some 10°F over much of the United States
•Sea level rise of 5 feet, rising some 6 to 12 inches (or more) each decade thereafter
•Dust Bowls over the U.S. SW and many other heavily populated regions around the globe
•Massive species loss on land and sea — 50% or more of all life
•Unexpected impacts — the fearsome “unknown unknowns”
•More severe hurricanes — especially in the Gulf
Equally tragic, a 2009 NOAA-led study found the worst impacts would be “largely irreversible for 1000 years.”

The single biggest failure of messaging by climate scientists (until very recently) has been the failure to explain to the public, opinion makers, and the media that business-as-usual warming results in impacts that are beyond catastrophic. For these impacts, terms like “global warming” and “climate change” are essentially euphemisms. That is why I prefer the term “Hell and High Water.”

Business-as-usual typically means continuing at recent growth rates of carbon dioxide emissions, which we now know would take us to atmospheric concentrations of carbon dioxide greater than 1000 ppm (see U.S. media largely ignores latest warning from climate scientists: “Recent observations confirm … the worst-case IPCC scenario trajectories (or even worse) are being realised” — 1000 ppm). We are at about 8.5 billion metric tons of carbon a year (GtC/yr) and, until the recent global economic recession, were rising about 3% per year.

What is less well understood is that even a very strong mitigation effort that kept carbon emissions this century to 11 GtC a year on average would still probably take us to 1000 ppm — a little noted conclusion of the 2007 Intergovernmental Panel on Climate Change (IPCC) report (see “Nature publishes my climate analysis and solution“).

The scientific community has spent little time modeling the impacts of a tripling (~830 ppm) or quadrupling (~1100 ppm) carbon dioxide concentrations from preindustrial levels. In part, I think, that’s because they never believed humanity would be so stupid as to ignore the warnings and simply continue on its self-destructive path. In part, they lowballed the difficult-to-model amplifying feedbacks in the carbon cycle.

So I pieced together those impacts from available studies and from discussions with leading climate scientists for my book, Hell and High Water. But now as climate scientists have sobered up to their painful role as modern-day Cassandra’s, the scientific literature on what we face is much richer. Let me review it here.


Two of the best recent analyses of what we are headed towards can be found here:

•M.I.T. joins climate realists, doubles its projection of global warming by 2100 to 5.1°C
•Hadley Center: “Catastrophic” 5-7°C warming by 2100 on current emissions path
As Dr. Vicky Pope, Head of Climate Change Advice for the Met Office’s Hadley Centre explains on their website (here):

Contrast that with a world where no action is taken to curb global warming. Then, temperatures are likely to rise by 5.5 °C and could rise as high as 7 °C above pre-industrial values by the end of the century.

That likely rise corresponds to roughly 9°F globally and typically 40% higher than that over inland mid-latitudes (i.e. much of this country) — or well over 10°F.

[Note: The MIT rise is compared to 1980-1999 levels see study here). So you can add at least 0.5 C and 1.0°F for comparison with pre-industrial temperatures.]

Based on two studies in the last few years:

By century’s end, extreme temperatures of up to 122°F would threaten most of the central, southern, and western U.S. Even worse, Houston and Washington, DC could experience temperatures exceeding 98°F for some 60 days a year. Much of Arizona would be subjected to temperatures of 105°F or more for 98 days out of the year–14 full weeks.

Yet that conclusion is based on studies of only 700 ppm and 850 ppm, so it could get much hotter than that.

And the Hadley Center adds, “By the 2090s close to one-fifth of the world’s population will be exposed to ozone levels well above the World Health Organization recommended safe-health level.”

The Hadley Center has a huge but useful figure which I will reproduce here:

[read the entire article]

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