Testimony Excerpted from Court Document

Hansen testified that human emissions of greenhouse gases, including carbon dioxide and methane, are climate “forcing” agents that can cause warming of the Earth’s surface. (10)

(10) A “forcing” is an imposed perturbation to the planet’s energy balance, measured in watts per meter squared. Tr. vol. 13-B, 10:2-10 (Hansen, May 3, 2007). Greenhouse gases absorb heat radiation, so that an increase in the amount of these gases in the atmosphere is a mechanism for making the Earth’s surface warmer. Such warming can be measured in the same way as other causes of temperature change, such as changes in the sun’s brightness. Id. at 12:16-24.

Tr. vol. 10 13-B, 12:7-8 (Hansen, May 3, 2007). Since pre-industrial times, there has been a drastic increase in atmospheric concentrations of such gases, due primarily to fossil fuel burning. (11) Id. at 11 13:8-14:3.

(11) The concentration of carbon dioxide in the ambient 11 atmosphere in the present time, averaged over the world, is about 383 parts per million, compared with 280 parts per million in the pre-industrial era. Id. at 13:8-13. This increase is due primarily to fossil fuel burning, which accounts for about eighty percent of the increase. To find carbon dioxide concentrations as high as current ones, it is necessary to look at a period two to five million years ago. Current annual increases in carbon dioxide emissions are two parts per million, up from one part per million when measurements began in 1958. They are predicted to rise to about four parts per million per year by the middle of the century under the business-as-usual scenarios. Id. at 58:15- 59:3.32

On long term scales, the climate is very sensitive to even small forces, and human-made forces are now much larger than the changes that drove glacial to interglacial changes in the past. Id. at 30:22-31:1.

Hansen’s “tipping point” theory posits that at a certain point the changes associated with global warming will become dramatically more rapid and out of control. The “tipping point” is the point at which very little, if any, additional forcing is needed for substantial changes to occur. Id. at 50:18-23. Hansen testified that based on the historical temperature record, drastic consequences, including rapid sea level rise, extinctions, and other regional effects, would be inevitable with a two to three degrees Celsius warming expected if no limits are imposed and emissions continue at their current rate. Such changes could happen quickly once a tipping point is passed. On the other hand, Hansen theorizes that if GHG emissions are reduced, warming may remain within the upper limit of previous interglacial periods and might avoid the most drastic consequences of global warming. See id. at 48:7-49:1.

In the last one hundred years the temperature has increased to within less than one degree Celsius of the warmest interglacial period in the past 1.3 million years. Id. at (12) 37:15-38:2.

(12) This data is from the temperature as measured in ocean cores.

Hansen testified that warming may be less dangerous as long as it stays within that range, and certainly it would have a less drastic effect than the warming that is expected if GHG emissions continue unchecked by regulation. He posits that an “alternative scenario” in which regulations are imposed to keep the temperature in that range is necessary. Id. at 38:4-13. (13)

(13) Hansen supports this conclusion by looking at the historical record. In the middle Pliocene period 3-1/2 million years ago, the temperature was two to three degrees Celsius warmer than the present global temperature, approximately the level of global warming that Hansen predicts absent regulation of greenhouse gases. Sea level rose twenty-five meters. Id. at. 28:3-9. During the past 1.3 million years, while temperature fluctuations were less dramatic, sea level was at least a few meters higher than today’s during some periods, but the rise was less drastic. Id. at 38:20-24.

Hansen testified that sea level rise is likely to take place in a nonlinear fashion because of multiple positive feedbacks (14).

(14) Feedbacks magnify the effect of a forcing. Even a very small forcing may have a large effect because warming will cause the release of carbon dioxide from oceans, increasing the forcing, and decrease ice cover, increasing the amount of warmth that is absorbed by the Earth rather than reflected. These feedbacks will cause still more carbon dioxide release and melting of ice. Id. at 22:22-23-1.

Id. at 52:7-20. Once a certain point is reached, rather than melting at a consistent rate, ice sheets may rapidly disintegrate. Hansen pointed to evidence in the paleoclimate record for such abrupt climate changes. Id. at 46:22-47:18. (15)

(15) For example, in the transition from the last ice age to the current interglacial period, there was a period in which sea level increased twenty meters in four hundred years, or about one meter every twenty years, a phenomenon known as Meltwater Pulse 1A. That ice sheet was at a lower latitude than the Greenland or Antarctic ice sheets, but was subject to a much smaller forcing. Id. at 47:7-18.

Huge changes, on the scale of one hundred meters of sea level rise, have frequently taken place over the course of only a few thousand years. There are multiple instances in which sea level has risen several meters per century, in response to smaller forcings than those currently underway. Id. at 51:8-21. Based on this record, Hansen’s opinion is that the time scale of the response of an ice sheet depends on the time scale of a forcing. Id. at 51:12-15. The scale of the GHG forcing currently underway shows that it is virtually certain that such a large-scale rise will occur if GHG emissions continue to increase. Id. at 52:7-20.

To support his testimony regarding ice loss, Hansen presented substantial data, including satellite observations and gravitational measurements from the GRACE satellite in Greenland and West Antarctica, showing patterns that suggest that ice sheets are both melting and becoming increasingly unstable. (16) Id. at 44:3-46:4; 119:11-120:5.

(16) Satellite observations support Hansen’s belief that the 16 Earth is at risk from ice sheet disintegration. Satellites show increasing meltwater on the ice sheet in Greenland during the
summers. Id. at 43:9-15. Icewater finds the lowest spot and burrows a hole through the base of the sheet, lubricating the base of the sheet and speeding the discharge of giant icebergs to the ocean. On the largest ice stream in Greenland, the flux of icebergs has doubled in the last five years. Id. at 43:25-44:2. The satellite GRACE, which measures the gravitational field of the Earth to show changes in ice sheet mass, shows that the ice sheet is melting faster than it is being increased by additional snowfall. Id. at 44:17-45:3. The frequency of earthquakes in Greenland has doubled between 1993 and 1999, and again between 1999 and 2005, a pattern consistent with a nonlinear process in which the ice sheet is becoming less stable. Id. at 45:11-46:4. The ice sheet of greatest concern is the West Antarctic Ice Sheet, which sits on bedrock, below sea level, in direct contact with the ocean. This ice sheet contains sufficient water that, if melted, could cause sea level to rise a total of seven meters. Its ice shelves are now melting several meters per year. Id. at 49:2-16.

Hansen also testified regarding likely regional climate changes resulting from global warming. Climate history underscores the likelihood of species extinction resulting from climate change; in the history of the Earth there have been five or six global warming events comparable to or larger than that predicted for the end of the 21st Century, each resulting in the extinction of a majority of the species on the planet. Id. at 69:13-23.

As to regional effects, climate models agree on an intensification of the climatic patterns of rainfall belt in the tropics and dry subtropical regions on both sides, leading to more intense dry conditions in the western United States and Mediterranean and parts of Africa and Australia. Id. at 56:24-57:11.

Addressing these problems, according to Hansen, means addressing emissions of carbon dioxide, the most important greenhouse gas (17),

(17) Although methane is a far more powerful greenhouse gas, it is not released in the same large quantities and does not have the same lengthy lifetime. A century after carbon dioxide is released a third of the carbon dioxide will remain in the
atmosphere. After five hundred years, a quarter will remain. Although some carbon dioxide is taken up by the ocean, carbon dioxide taken up by the ocean exerts a back pressure on the atmosphere, so a significant fraction will remain in the atmosphere until that previously taken up has been deposited in the sediments of the ocean, a process taking thousands of years. Id. at 29:10-30:12.

through an alternative scenario. Id. at 25:5-10. That scenario contemplates an initial slow decrease in carbon dioxide emissions followed by more rapid decreases later in the century as new technologies are developed. Id. at 59:6-63:1. The vehicle emissions reductions that the GHG regulation requires are consistent with the alternative scenario’s conception of the necessary steps to check global climate change before the Earth reaches a tipping point leading to the disastrous results described above. (18)

(18) Hansen and his students used the National Research Council report on vehicle efficiencies to determine how vehicle emissions reductions could fit in with such a scenario. By taking the improvements outlined in that report that would basically pay for themselves and forecasting a phase-in of those recommendations over a ten year period, they found that with the expected growth in vehicle numbers, those improvements actually cause a moderate decrease in total vehicle emissions, which continues for a few decades without further improvements. Id. at 63:2-64:1. That report used slightly weaker emissions requirements than those that the regulation imposes. Id. at 67:20-68:8.

Hansen did not testify that GHG regulations such as Vermont’s will solve the global warming problem. Id. at 71:24-72:4. Rather, he testified to his opinion that the Vermont regulations’ emissions reductions are scientifically important, not because of their effects when taken alone, but because they are consistent with the rates of change necessary to avoid the most drastic consequences of global warming. Id. at 72:18-73:2. Hansen testified that it is hard to say what straw will break the camel’s back in terms of tipping points. Id. at 73:6-12. In addition, he noted that the effects of the regulation may be magnified if its adoption encourages reductions in other parts of the country and the world. Id. at 73:16-21.

If the alternative scenario is to be achieved, action must be immediate. One more decade of business as usual--that is, another ten years of two percent increases in carbon dioxide
emissions annually--would lead to emissions in 2015 that are thirty-five percent greater than those in 2000. It would then be virtually impossible to reduce emissions to the level necessary to meet the alternative scenario. Id. at 69:24-70:7.