In 2009 the director of NASA’s Goddard Institute for Space Studies, James Hansen, published Storms of My Grandchildren: The Truth about the Coming Climate Catastrophe and Our Last Chance to Save Humanity. One of the world’s most distinguished climate scientists, Hansen has been writing and speaking for years about the dire threat posed to civilization by global warming.

In fact, this self-described “slow-paced taciturn scientist” from a conservative Midwestern background has become so concerned about the impending threat that he has been arrested several times for protesting at strip-mining sites—and last August he was arrested, along with twelve hundred others, in an act of civil disobedience at the White House, protesting the proposed Keystone XL pipeline. The pipeline would transport tar-sands oil—whose extraction and refining produces up to 30 percent more greenhouse gases than conventional oil—from Canada to the United States.

Why would someone like Hansen, a well-established professional and government employee, engage in civil disobedience? After all, “climatologists, like other scientists…are not given to theatrical rantings about falling skies,” writes Lonnie Thompson, himself a renowned climatologist at Ohio State University. Yet Hansen, Thompson, and many others are attempting to make a dent in attitudes that are preventing Americans from recognizing and addressing what Thompson says virtually all climatologists are now convinced of—namely, “that global warming poses a clear and present danger to civilization.” While those who deny that the planet is warming and/or that humans are the primary cause form a distinct minority in this country, representing only 26 percent of the U.S. population—and only 2 percent of those who publish in climate science—a passive or reluctant majority remains unaware of the magnitude and urgency of the problem.

Climate change, however, is not just another big national problem—like long-term unemployment, health-care costs, or the national debt—that can be kicked down the road and solved later. Rather it is, according to Hansen, a “planetary emergency,” and delay beyond a certain critical moment will entail irreversible effects, including what Lonnie Thompson calls “rapid and potentially catastrophic changes in the near future.” Having such a desperate future presented to them leaves many people incredulous, a reaction that the American Psychological Association, in its report Psychology and Global Climate Change, refers to as “denial in the face of overwhelming and uncontrollable risk.” Yet there is no escaping the scientific evidence. We are already experiencing large impacts—from only .8°C (1.4°F) of warming. And scientists are forecasting another 5 to 7°C (9 to 12.6°F) of warming over the remainder of this century.

The situation is not yet beyond saving; it is still possible for us to shift rapidly to clean energy. But doing so will require dramatic political action. There is a lot of lost ground to make up. Since the nineteenth century, the amount of atmospheric carbon dioxide (CO₂)—the major heat-trapping gas—has increased from 280 parts per million (ppm) to 390 ppm. This seemingly slight rise in temperature has almost certainly boosted the frequency and intensity of extreme weather events over the past decade, as increased evaporation from higher temperatures dries out some areas and (by increasing atmospheric water vapor) causes intense storms in other areas. For example, in 2010—tied with 2005 as the warmest year on record—Nashville, Tennessee, experienced massive flooding that killed more than twenty people and caused widespread damage. That same year, northwestern Pakistan received 16.5 feet of rain over a five-day period. The resulting floods killed 1,600 people, leaving 16 million homeless, and destroying 6 million acres of crops. In December 2010, Australia experienced unprecedented flooding that covered an area the size of Germany and France combined.

Brazil, France, Sri Lanka, Mozambique, the Philippines, and South Africa all experienced extraordinary flooding events in 2010; the flooding in South Africa led to one of its smallest winter wheat harvests in twenty years. While South Africa’s wheat crop was being battered by excessive rain, Russia (the world’s third-largest wheat exporter) lost 40 percent of its wheat harvest to July temperatures 14°F above the norm. That heat wave, according to the Earth Policy Institute, led to the death of 56,000 people and to $300 billion in damage from forest fires. In the fall of 2010, China’s Shandong Province experienced its worst drought in two hundred years, spurring the UN Food and Agriculture Organization to issue a special alert about major potential shortfalls in China’s wheat crop and the cascading effects on food prices around the globe. These extreme events led to an 80-percent increase in the price of wheat, which in turn fueled instability in the Middle East. And on and on.

Because of the long life of CO₂ , unless we immediately reduce greenhouse gas emissions by at least 60 percent globally—that is, down to the level at which land vegetation and the oceans remove these gases from the atmosphere—we can expect more extreme climate impacts for at least the next thousand years. In fact, since we are clearly not going to reduce greenhouse emissions immediately by 60 percent, it is probably already too late to save the summer sea ice in the Arctic. The Arctic in summer could be virtually ice-free by as early as 2015, and totally ice-free by 2040. A dark, open Arctic Ocean will absorb a great deal more of the sun’s energy, which will further increase global warming. This in turn will increase the melting of the permafrost, which will release CO₂ and methane (a greenhouse gas far more potent than CO₂). It is estimated that the complete melting of the permafrost alone could increase warming by 4°C (7.2°F).

Meanwhile, the Amazon suffered extreme droughts in both 2005 and 2010, losing millions of trees. As those trees decompose, they will release an amount of CO₂ equivalent to nearly 42 percent of the world’s emissions in 2009; such events, repeated over time, could turn the Amazon rainforest from a “carbon sink”—an important resource for drawing CO₂ out of the atmosphere—to a significant source of CO₂. These are but a few examples of “positive feedbacks,” large-scale changes that will increase future warming. Increased greenhouse gas emissions can push the climate system or elements of the system to a tipping point where the dynamics of the system take over and cause very large changes that are completely beyond our control.

When we consider that only .8°C of warming has caused such large-scale changes, projections in the scientific literature of the effects of our current emissions path and the corresponding temperature increase of 5 to 7°C (relative to preindustrial temperatures) appear much more believable. What will such a temperature increase mean for the human community? Let me follow the personal cue in the title of James Hansen’s book, Storms of My Grandchildren, and travel into the future of my sons, currently ages eight, six, and two, to see what sort of world they might find themselves growing older in.

Two decades from now, when my sons are in their twenties, CO₂ levels are projected to reach 450 ppm. At that point the Southwestern United States, Southern Europe, Northern Africa, Southern Africa, and Western Australia could be dustbowls. Social stability will be rocked by refugees from Mexico and Central America, fleeing drought conditions and sharp reductions in crop yields—reductions that will extend across the tropics and subtropics, where most of the world’s poor live. When my sons enter their thirties in the 2040s, the destruction of the world’s coral reefs from warmer and more acidic oceans caused by CO₂ absorption will be well underway. According to the marine scientist J. E. N. Veron, “once-thriving coral gardens that supported the greatest biodiversity of the marine realm will become red-black bacterial slime”—an essentially irreversible loss, since it would take hundreds of thousands or even millions of years for the chemistry of the oceans to return to a state supportive of coral reefs. The collapse of coral reefs, moreover, may exert a domino effect, triggering a mass extinction of ocean ecosystems.

When my boys enter their forties—perhaps by now with children of their own—CO₂ levels will likely have reached 560 ppm. The global water crisis will contribute to a global food crisis, with insufficient fresh water for irrigating crops. By this time, many of the world’s mountain glaciers, which feed the rivers that provide water for half the world’s population, will be substantially diminished or gone. The shrinkage of the Sierra Nevada snowpack will have greatly impaired California’s agriculture, which today produces nearly half of U.S.-grown fruits and vegetables. Corn and soy yields in the United States, currently a major contributor to world markets, will experience drastic declines. Forests throughout the western United States will burn, with California losing 50 to 70 percent of its forests. The Amazon rainforest will suffer devastating drought-driven fires. Seas worldwide will have risen one foot, and coastal cities will enter the first phase of their destruction.

By the 2060s, if carbon-cycle feedbacks prove to be strong, the world could be 4°C warmer, and 40 to 70 percent of assessed species could be headed irreversibly toward extinction. And by the end of the century, my grandchildren and great grandchildren will live in a world where sea levels could be between three and seventeen feet higher than they are now. The abandonment of many of the world’s great cities will be well underway. Food markets could see an 80-percent reduction in U.S. corn and soy yields and the collapse of California agriculture. Half the forests in the American West could be gone, destroyed by fire.

When faced with the overwhelming character of these forecasts, we develop coping mechanisms (as multiple studies in psychology and climate change have shown) that shield us from the real gravity of our situation. This is understandable, and to some extent we are all to a certain degree susceptible to this, since a real acceptance of the science requires one to fundamentally revise one’s understanding of the world and one’s responsibilities to it. That is not easy to do.

Climate change is complex, people say; the science is uncertain. That there will be large destructive changes from the continued warming of the planet is certain; indeed, it is already happening. Yet we cannot know with certitude precisely how large and rapid these changes will be. What is clear, though, is that so far we have substantially underestimated the problem. The polar ice sheets, for instance, are melting 100 years ahead of the 2001 forecasts of the Intergovernmental Panel on Climate Change (IPCC). The rate of sea-ice melt in the Arctic is thirty years ahead of the 2007 IPCC projections. Carbon dioxide pollution is raising ocean acidity ten to twenty times faster than models predicted. And many of the feedbacks that will increase warming have not been included, or are just beginning to be included, in computer models. My description of the possible future of my sons, for instance, does not include the melting of the permafrost, which is likely to start significantly increasing warming in fifteen to twenty years.

The worst of this future is avoidable, but only if planetary warming does not increase more than 2°C relative to pre-industrial levels. To have a two-thirds chance of holding this 2°C line, developed countries like the United States will have to stop CO₂ emissions growth this year and reduce their emissions approximately 11 percent per year toward near-total decarbonization by 2050. To grasp the staggering scale of this challenge, one should merely note that the only instance of national or regional emission reductions greater than 1 percent per year over a ten-year period occurred during the economic collapse of the former Soviet Union, when emissions declined 5.2 percent per year—and it required a halving of the economy to get it done.

What happens if we take a less radical—and more politically palatable—emissions-reduction path? If we assume that the developed world can halt the growth of its emissions by 2016, followed by a 3-percent reduction in emissions per year, and we include in this analysis those greenhouse-gas emissions that cannot be reduced to zero (for example, nitrous oxide and methane involved in food production), then the world will likely warm by nearly 4°C by 2100. And this analysis, from Alice Bows and Kevin Anderson of the Tyndall Centre for Climate Research in the UK, does not include the most dangerous positive feedback, the melting of the permafrost—which, it is estimated, will eventually increase warming by approximately 4°C. Figure that in, and humanity will likely find itself living in the nightmare world I sketched above. Kevin Anderson has expressed the gravity of our situation, calling our chances (in a world 4°C warmer) of avoiding mass death—the loss of more than 90 percent of human beings—“extremely unlikely.” This is not the opinion of a crackpot, but rather the judgment of the director of a major international climate center.

The United States has been the chief obstacle to all the significant attempts to avoid this fate. Despite being the largest historical emitter, responsible for 27 percent of the fossil fuel CO₂ emissions in the atmosphere since 1750 (China is second at 9 percent and India third at 2.7 percent), the United States has been the main barrier to moving the world away from a fossil-fuel-based economy. We never signed the Kyoto Protocol, and our credibility in international negotiations, such as those at Copenhagen in December 2009, has been undermined by our failure to pass domestic climate legislation. This failure is not due to a lack of public support. According to the polling of Stanford social scientist Jon Krosnick, three-quarters of all Americans want the federal government to limit businesses’ greenhouse-gas emissions. Yet those who support climate legislation (including some large corporations) have not been able to compete with the U.S. Chamber of Commerce, the fossil-fuel industry, and the many electric utilities that spent more than $540 million in 2009–10 to lobby against such legislation.

While Republicans and some conservative Democrats in the Senate are ultimately responsible for not passing climate legislation, President Barack Obama has never used the bully pulpit of his office to address the nation about the seriousness of the endeavor, and he never put the weight of his office behind the Democratic effort to push a climate-change bill through the Senate after it had passed the House. The bill failed—and consequently, as Al Gore had predicted, the Copenhagen Conference did, too. As the conference was ending, Obama did help lead an effort to establish a nonbinding accord. But the carbon-reduction proposals put forth so far in the working-out of that accord will likely commit us by 2100 to a world 4.5°C warmer. As for our domestic legislative efforts, since the 2010 election matters have gotten worse. In unanimously voting against an amendment to accept the scientific consensus on climate change, Republicans on the House Energy and Commerce Committee have made official what has long been true in practice, that the Republican Party is the only major political party in the world that rejects the “settled fact” (the words of the U.S. National Academy of Sciences) that human beings are the primary drivers of a warming planet.              

The failure of our political system to address this global emergency is alarming. Yet it is important to recognize that we can still avoid irreversible catastrophic climate change. With existing technology, we could harness solar and wind energy to produce over forty times the power needed for the entire world. According to Stanford’s Mark Jacobson, a leading researcher in this field, “There are no technological or economic barriers to converting the entire world to clean, renewable energy sources. It is a question of whether we have the societal and political will.”

Our task in the United States is to use all means at hand to bolster and direct that will—to inform and organize people so that, as the climate begins to deteriorate over the next decade, citizens will rise up and reject what UN Secretary-General Ban Ki-moon calls the “global suicide pact.” We have a moral responsibility to join together in our communities—universities, hospitals, parishes, dioceses—and communicate to our elected leaders (and to businesses that fund opposition to climate legislation) that we do not intend to be complicit, through silence, in the mass death of human populations and the mass extinction of species.