There has been a shift in the climate debate over recent months. It seems people are talking less about the science and more about the alleged actions of a small group of climate scientists. Senator Inhofe is an extreme example with his recent attempt to criminalize 17 leading scientists. These accusations are largely based on stolen private emails that are being quoted out of context and/or without understanding of the science involved. Unfortunately, this is shifting the focus away from the most important element of the climate debate: the scientific reality of global warming. The empirical evidence that global warming is happening and that humans are the primary cause has been and continues to be observed, measured and documented in the peer-reviewed scientific literature.
We find out what's happening in our climate by empirical observations - measurements made out in the real world. We have even more confidence in our understanding when independent measurements find the same result. In the case of man-made global warming, we have multiple lines of evidence that global warming is happening and that human activity is the predominant cause. There are not only independent scientific teams all over the globe but also measurements of a wide range of phenomena all painting the same picture.
Atmospheric carbon dioxide is increasing. This is measured by hundreds of monitoring stations across the globe, all finding the same increasing trend (NOAA). The rising trend is confirmed by satellite measurements conducted independently by NASA, the European Space Agency and the Japan Aerospace Exploration Agency. Combined with ice core measurements from Greenland and Antarctica, this tells us that atmospheric CO2 levels are the highest in over 15 million years (Tripati 2009).
What's causing rising CO2? We can use energy statistics to calculate human CO2 emissions at around 29 billion tonnes per year (CDIAC). In contrast, atmospheric CO2 is rising by 15 billion tonnes per year. Humans are emitting nearly twice as much CO2 as ends up remaining in the atmosphere. Measurements of carbon isotopes confirm that the rising CO2 originates from the burning of fossil fuel (Ghosh 2003). Further independent confirmation comes from observed falling oxygen levels caused by the burning of fossil fuel (Manning 2006).
What's the effect of all this extra CO2? Satellite measurements of outgoing longwave radiation find an enhanced greenhouse effect (Harries 2001, Griggs 2004, Chen 2007). This result is consistent with measurements from the Earth's surface observing more infrared radiation returning back to the surface (Wang 2009, Philipona 2004, Evans 2006). Consequently, our planet is experiencing a build-up of heat (Murphy 2009).
This heat build-up is manifesting itself across the globe. Arctic sea-ice loss is accelerating beyond the worst case scenarios of model forecasts (Stroeve 2007). Antarctic and Greenland ice sheets are losing ice mass at an accelerating rate (Velicogna 2009). This is speeding up sea level rise as observed by tidal gauges and satellite altimeters (Church 2006). Spring is coming earlier each year (Stine 2009). This leads to observed changes in animal breeding and migration (Parmesan 2003). Distribution of plants are shifting to higher elevations (Lenoir 2008).
How will global warming affect humanity? For brevity's sake, let's focus on just one impact. The latest research that takes into account accelerating ice loss estimates sea level rise by the end of this century of between 75 cm to 190 cm (Vermeer 2009). An independent study of glacier ice dynamics predicts similar results (Pfeffer 2008). Studies of Earth's climate 125,000 years ago find that sea levels were at least 6 metres higher than today (Kopp 2009). Global temperatures were around 2°C warmer - this is the amount of warming expected for some of the IPCC's lower emission scenarios. This provides additional evidence that the Greenland and Antarctic ice sheets are highly sensitive to sustained warmer temperatures.
Senator Inhofe is trying to distract us from the unpleasant reality: within the lifetime of our children and grandchildren, they'll witness sea level rise of around 1 to 2 metres. To hope to mitigate against such a future, it's imperative that the climate debate returns to a focus on science. Scientists need to do better at communicating their research to the public. Skeptics who are genuinely seeking scientific truth need to search the peer-reviewed literature to obtain the broader picture. The stakes are too high to be distracted by political manoeuvring and ad hominem attacks.
Posted by John Cook on Friday, 26 February, 2010
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