When NASA's top climatologist, James E. Hansen, was silenced  because his research on global warming  was at odds with Bush Administration policies, he became a cause célèbre for browbeaten scientists fed up with the government stranglehold on their research.
It's fitting, then, that he was a last-minute addition to the recent Conference on Politics and Science, hosted by the journal Social Research  at the New School, where leading scientists and policy experts discussed the politicization of science and the urgency to address the consequences of global climate change.
Hansen has largely ignored the media for the past fifteen years, slightly less than half his tenure at NASA. But after a presentation in December on global warming to the American Geophysical Union (AGU) in San Francisco, he began to feel an even greater restraint on the public dissemination of his research.
"I think the reason was that my talk was very wide-ranging, connecting the dots from emissions to climate change and to impacts and what you need to do if you want to get on a scenario that reduces climate change," Hansen said. "The public affairs people just didn't like that and started bouncing off the walls, as I've been told."
Hansen's current research explores the relationship between greenhouse gases and changes in temperature and sea level over the past 400,000 years. Climate scientists have looked for this sort of paleoclimate data for decades because it strengthens the argument that the earth's current warming cycle is predominantly influenced by our carbon dioxide emissions.
He explained that records of atmospheric carbon dioxide, methane and temperature for the past 400,000 years, taken from Antarctic ice cores, revealed the difference between the warmest interglacial periods and the depths of the Ice Age to be about five degrees on global average.
This, along with detailed sea-level data, also from the past 400,000 years, can measure climate sensitivity. When applied to the present interglacial period, which is the warm period that has existed for the past 10,000 years, the interplay and necessary balance between ice and greenhouse gases becomes clear.
"If the planet were out of balance by even one watt per square meter for 1,000 years, it would melt all the ice on the planet or raise the ocean temperature an implausible amount," Hansen said.
And that is exactly where the earth is headed: Current fossil fuel carbon dioxide emissions increase about 2 percent each year; if this continues, temperatures will increase between two to three degrees Celsius by the end of the century.
This last occurred about 3 million years ago, when the earth was a much different place. The East Coast, for instance, was nearly 100 kilometers inland; Florida was completely underwater.
"The greenhouse gas changes that humans have introduced in the past century are far outside the range that has existed for hundreds of thousands of years, and they will remain so for centuries because of the long lifetime of these gases," he explained. This means the gases were added so quickly that the planet has not had time to respond and, therefore, is out of balance.
"Humans now control the global climate, for better or worse," he said. Earth is approaching a tipping point that can be tilted, and only slightly at best, in its favor if global warming can be limited to less than one degree Celsius. Paleoclimate data shows past interglacial periods were about one degree warmer than today, raising the sea level by as much as five meters.
Sea level may not be important in our lifetime, but it will be in the long run--and it's very difficult to get people to take it seriously, Hansen said.
One way to get people to focus on the implications of this climatic sea change is to focus on its impact on human health. Rita Cowell, former director of the National Science Foundation and now a distinguished professor at the University of Maryland, noted that cholera, a major problem in India, is strongly correlated to the rise in sea surface temperature and sea surface height.
"When we discuss climate change, we are discussing biological interplay," Cowell said. "And when you read about climate change and the predictions that can occur, I want you to think about people, and ourselves, as part of the human race, and the effects it will have on us."
Government suppression of politically inconvenient scientific inquiry undermines the urgency of research by scientists like Cowell and Hansen. And NASA, Hansen noted, is not the only agency that has put a political spin on science: Hansen took aim at the National Oceanic and Atmospheric Administration (NOAA) for failing to recognize clear evidence of the link between increasing ferocity of tropical storms and greenhouse gases.
"We calculate an ocean surface warming in the region of hurricane formation, caused by human-made climate forcings," Hansen said. "So the categorical contention of the NOAA National Hurricane Center that recent hurricane intensification is due to a natural cycle of Atlantic Ocean temperature, and has nothing to do with global warming, is irrational. How could a hurricane distinguish between natural and greenhouse-gas warming?"
Hansen acknowledged that the topic is quite complex and still being explored by the scientific community, but he added that it seems "the public, by fiat, received biased information." Hansen asserted that NOAA scientists "were told not to dispute the hurricane conclusion in public" and that many of his colleagues at NOAA have told him their conditions are, in general, much worse.
"A NOAA scientist cannot speak with a reporter unless there is a 'listener' on the line with him or her," Hansen said, adding, "it seems more like Nazi Germany or the Soviet Union than the United States. The claim is that the 'listener' is there to protect the NOAA scientist. If you buy that one, please see me at the break; there is a bridge down the street that I would like to sell to you."
Hansen remains optimistic about his own freedom at NASA, saying the agency has assured him it is committed to fixing the problem and that he hopes NASA becomes the model for other agencies to follow. Political interference, he noted, has always been an issue for scientists, regardless of what party is in power.
Hansen's sense of responsibility for his research stems largely from the first line of NASA's mission statement: "To understand and protect our home planet."
"The point I made to my boss and his boss is, We're not doing our job if we don't make clear this information," Hansen told reporters. "Not every scientist is in a position to look at this picture and feel that we have some understanding of it from the emissions to the end consequences, and it would be inappropriate to not make that clear."
Hansen's research boils down to one very straightforward point: We can still avoid the dangers of human-made climate change, but only if we focus our attention on cutting near-term emissions by improving fuel efficiency. As the world's largest emitter of carbon dioxide, the United States must lead the effort if developing countries like India and China can be expected to follow.
"We are not now on a path to do that," he says, "and if we do not begin actions to get on a different path within the next several years, we will pass a point of no return."