UNDERSTANDING THE CLIMATE CATASTROPHE

One of his most impressively forthright presentations was to the Club of Rome General Assembly. He titled it Global Warming Time Bomb: Actions Needed to Avert Disaster.

Hansen went straight to crux in this presentation pointing out the knowledge gaps regarding what is understood (by scientists) and what is known (by the public and policymakers).

He's what Hansen had to say starting with the climate tipping points of special concern.

"Tipping points are "non-linear" phenomena, which means that they can reach a point at which rapid catastrophic change occurs. It is inherently difficult to determine the time at which non-linear collapse will occur, even in cases where such rapid change is certain.

"The mechanism that seems to be most important for disintegration of the great ice sheets that cover Antarctica and Greenland begins with ocean warming. Ocean warming leads to melting of ice shelves, which are tongues of ice that stretch out into the ocean. The ice shelves buttress the ice sheets, so when ice shelves disappear the more mobile parts of the ice sheet, the ice streams, can surge into the ocean ? thus removal of the ice shelves is somewhat akin to taking the cork out of a bottle ? it allows the material behind to flow rapidly. We know from Earth's history that once ice sheet disintegration is well underway, sea level can rise by several meters per century.

"Species extermination is also a non-linear problem. Today we are placing many species under multiple stresses, but one stress that is growing rapidly is the shifting of climate zones due to global warming. An average temperature line has been moving poleward at a rate of 50-75 kilometers per decade during the past three decades. As the total movement of climate zones becomes larger it threatens those species that are less mobile. Because of interdependencies of species, the loss of key species can cause entire ecosystems to collapse.

"Methane is an especially powerful greenhouse gas. There are large amounts of methane presently locked up, frozen, in high latitude tundra and, especially, in ocean sediments on continental shelves. We know from Earth's history that this frozen methane can be released suddenly by sufficient warming ? thus this methane has the potential to greatly amplify human made global warming, if that warming reaches a level, a tipping point, such that large volumes of frozen methane begin to melt.

"Arctic sea ice is another potential tipping point of the climate system. The area of sea ice at the end of the summer began to be measured accurately from satellites in the late 1970s. The graph shows that the area of sea ice fluctuates from year to year, based on variable weather patterns. However, overall there has been a decline in sea ice area over the past three decades. In 2007 there was a sharp decline of sea ice area, to an amount just over half of the ice area three decades earlier.

"Although sea ice recovered slightly in 2008 and even more in 2009, most analyses indicate that all summer sea ice will be lost within the next few decades, if business-as-usual greenhouse gas increases continue. It is difficult to imagine that the Greenland ice sheet could survive, if the Arctic sea ice disappears in summer.

"Stabilization of Arctic sea ice requires, to first approximation, that Earth's energy balance is restored. At present, because human-made greenhouse gases have reduced the amount of heat radiation that Earth is emitting to space, the planet is out of energy balance by about 0.5 watts per square meter, uncertain by about 0.25 watts per square meter. Other things being equal, the amount of carbon dioxide in the air would need to be reduced from its present 387 ppm (parts per million) to about 350 ppm in order to increase emission of heat radiation to space by 0.5 watts per square meter and restore Earth's energy balance."

Hansen went on to emphasize the intergenerational inequity of global warming.

"My grandchildren began to influence me when I realized that policy makers were ignoring the message from the climate science, or rather that politicians were developing the fine art of greenwash, they would say favorable words about the environment and stabilizing climate but their actions were inconsistent with that goal.

"Politicians would be happy if scientists just tell them there is a climate problem and then go away and shut up ? let them decide what they want to do. But I decided that I did not want my grandchildren, some day in the future, to look back and say "Grandpa understood what was happening, but he did not make it clear."

What Hansen says is crystal clear that the human species cannot burn all the fossil fuels, as there is a limit on how much carbon can put into the atmosphere.

All the scientific evidence, according to Hansen, "tell us unambiguously that we must phase out all coal emissions rapidly, not develop the unconventional fossil fuels, and not even go after every last drop of oil on the planet. In that case, our children and grandchildren have a chance of inheriting a planet that is not spiraling out of their control."