CO2 and Global Warming
Here are a few graphs that show the connections between CO2, temperature, fossil fuel emissions, and changes in our climate. Certainly, CO2 represent just one of several important greenhouse gases, but it’s easiest to focus on here.
Here’s recent temperature deviations from Brohan etal (2006). Each point is a global average, and the error bars are the coldest/warmest months of each year.
We’ve increased 1C over the last century.
Here are fossil fuel emissions plotted on top of recent CO2 concentrations in the atmosphere (data come from a variety of sources including Marland et al 2008).
Humans increased atmospheric CO2.
The following plot shows the connection between CO2 and temperature over the last 400,000 years, obtained by analyzing ice cores (Petit et al 1999).
When people say there are natural variations to climate, yes, it’s true. It’s also true that humans weren’t responsible for these variations: Essentially, a wiggling Earth/Sun orbit is thought to be the driver. But this driver has nothing to do with the changes over the last 200 years.
Underlying these greenhouse gas concentrations and warming trends are the energy fluxes from the Sun and subsequent pathways through our atmosphere. Here’s a great figure from Kiehl and Trenbreth (1997):
Changing the atmosphere’s chemical composition via our emissions, or even by adding reflective dust in the upper atmosphere, ever so slightly alters the balance at each one of these steps.
Different atmospheric components apply different “forces” to global warming, here summarized in a plot by the IPCC Physical Science report:
CO2 has the greatest forcing, though other chemicals might have a greater per-molecule forcing. Note the total forcing is around 1-2 Watts per square meter, compared with 168 W/m2 solar energy hitting Earth’s surface in the previous plot. That’s about one percent. Don’t let mentions of solar output, like this IPCC plot,
sow doubt about global warming: Yes, solar output varies, but climate scientists know and understand that fact. These solar output variations are less than one-tenth of one percent.
Those changes result in climate change. Furthermore, how a warming Earth changes soil respiration, for example, represents one of many “feedbacks” that makes climate predictions difficult.
And, so, what happens as a result? This plot shows that trees are flowering earlier (Roetzer etal 2000), as much as a month in some places.
Birds are laying their eggs a couple of weeks earlier (Dunn and Winkler 1999; this data might be updated somewhere).
That’s just a short overview of a small part of the science that exists demonstrating global warming. As with everything, there remain unknowns. There’s nothing political about it. It is clear that emissions have warmed Earth, changed climate, and will continue to make changes. End of story. Let’s stop emissions.
Brohan, P.et al. 2006. Uncertainty estimates in regional and global observed temperature changes: A new data set from 1850. J. Geophys. Res. 111:D12106.
Dunn, P.O., and D.W. Winkler. 1999. Climate change has affected the breeding date of tree swallows throughout North America. Proc. Roy. Soc. Lond. B 266: 2487-2490.
Kiehl, J.T., and K.E. Trenberth. 1997. Earth’s Annual Global Mean Energy Budget. Bull. Amer. Meteor. Soc. 78: 197-208.
IPCC, 2007: Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment
Report of the Intergovernmental Panel on Climate Change [Solomon, S., D. Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt,
M. Tignor and H.L. Miller (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, 996 pp.
Marland, G., R.et al. 2008. Global CO2 Emissions from Fossil-Fuel Burning, Cement Manufacture, and Gas Flaring: 1751-2005. Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory.
Petit, J.R. et al. 1999. Climate and atmospheric history of the past 420,000 years from the Vostok ice core, Antarctica. Nature 399:429-436.
Roetzer, T., M. et al. 2000. Phenology in central Europe: differences and trends of spring phenophases in urban and rural areas. Int. J. Biometeorol. 44:60-66.