Our Climate Future: Looking Back to See Aheadby Bill Chameides | January 20th, 2011
posted by Erica Rowell (Editor)
Permalink | 2 comments
Conditions millions of years ago may tell us where we are headed.
Climate models can be used to predict future climate trends but, as has been pointed out many, many times, models are far from the real thing. How accurate are such predictions? Hard to say.
But models are not the only way to peek into the future. There’s an old saw that the past is the key to the future and that is almost certainly true of the climate. For example, consider the question on most climate scientists’ minds these days:
How will the climate respond in the coming decades to rising carbon dioxide (CO2) concentrations from burning fossil fuels?
One answer comes from looking at past climatic conditions when CO2 concentrations were as high as we expect them to grow now.
A Look at Some Past Climate Numbers
So what does such a look into the past tell us? In a Policy Perspective piece published last week in the journal Science, Jeff Kiehl, of the National Center for Atmospheric Research, provided a pretty stark picture of rather hot times ahead. How so? Here are some of the numbers.
- Current global average temperature (in degrees Fahrenheit): 58.12 1
- 20th century average global temperature (in degrees Fahrenheit): 57 1
- Current CO2 concentration (in parts per million): 389 2
- CO2 concentration in 2100 under business as usual (in parts per million): 900–1100 3
- Last time on Earth CO2 reached ~1000 ppm: about 35 million years ago 4
- Global average temperature 35 million years ago (in degrees Fahrenheit): 88 5
The kicker? Climate models predict much less warming from a CO2 concentration of 1000 ppm. In other words, the empirical data from 35 million years ago suggest that the climate models underestimate the climate’s sensitivity to greenhouse gases like CO2.
Predicting future climate using models may put us on thin ice. But past climatic variations suggest the ice may be a whole lot thinner than we thought.
1. “State of the Climate Global Analysis Annual 2010,” NOAA’s National Climatic Data Center.
2. “Trends in Atmospheric Carbon Dioxide,” November 2010, NOAA’s Earth System Research Laboratory.
3. “Climate Change 2007: Working Group I: The Physical Science Basis,” IPCC Fourth Assessment Report.
4. “A Climate Debate,” September 29, 2010, TheGreenGrok.
5. “Early Palaeogene Temperature Evolution of the Southwest Pacific Ocean,” Peter Bijl et al., August 2009, Nature.filed under: carbon dioxide, carbon dioxide emissions, climate change, faculty, global warming, science, Statistically Speaking, temperatures
and: climate, climate models, climate science, greenhouse gas emissions, greenhouse gases