Clyde Burnett, Peak to Peak.  The accepted goal for a limit to global warming has been 2o Celsius, which we have assumed will allow us to mitigate the human-caused, increased greenhouse effect and make the necessary climate change adaptations. We are presently at 0.85oC with 400 ppm CO2. An IPCC model, recognized as conservative, predicts a sea level rise of 0.74 meters by 2100.

A recent publication, “Ice melt, sea level rise and superstorms: evidence from paleoclimate data, climate modeling, and modern observations that 2o C global warming is highly dangerous”, by Hansen, J.E. and coauthors (Atmos.Chem.Phys. disc 23 July 2015) disputes this assumption. Dr. James Hansen, formerly Director of the NASA Goddard Institute for Space Studies, is an Adjunct Professor at Columbia University’s Earth Institute. Hansen first testified before Congress in 1998 that we have a serious problem of global warming. In his 2009 book, Storms of My Grandchildren-The Truth About the Coming Climate Catastrophe and our Last Chance to Save Humanity- and in the above research publication, he states that temperature increase is a poor and dangerous limit; it is more appropriate to consider the Earth’s energy imbalance that is driven by the atmospheric greenhouse effect of carbon dioxide. The carbon dioxide control of heat trapping should be limited to an atmospheric concentration of 350 ppm.

Hansen proposed in 2005 that the warmed ocean waters influenced the rapid Greenland glacial melt. Now he refers to an analysis of climate in the Interglacial period 120,000 years ago with global temperatures increasing near 1o C, resulting in rapid ice melt with a sea level rise of 6-9 meters. This is explained by accelerated melting by warm ocean water and meltwater feedback; onsite observations indicate that it is presently an active process. The glacial meltwater forms a freshwater layer floating on the ocean, which traps the subsurface warmed ocean water and increases the melting, which increases the fresh meltwater layer. This also produces a misleading low temperature at the ocean’s surface, trapping of the dissolved CO2, and lengthening of this ocean-atmosphere cycle.

The dangers of a 20-30 ft sea level rise to the Earth’s coastal cities would be catastrophic. Hansen believes that the 2o C limit should be abandoned for a CO2 limit of 350 ppm with immediate implications for policy.

Question: But isn’t climate change supposed to be about weather extremes?

Answer: That is just one of the planet’s eventual responses to the energy imbalance. We already have a warmer ocean that evaporates increased water vapor, producing more heat trapping and increased precipitation in the water cycle. This has resulted in the costly 1000-year flood that closed all our canyons, New Jersey’s Hurricane Sandy, and the recent South Carolina statewide flood. In 2015 the warmed Pacific has generated almost 20 named tropical storms, including the recent cat 4 Super Typhoon Koppu in the Philippines with 42 inches of rainfall and 58 deaths, and the 200 mph cat 5 Hurricane Patricia, striking Mexico from the Eastern Pacific. Now we have a resurgence of Texas flash floods and the 5 ft deep mudslides on California Highway 58 and Interstate 5, and El Nino is just getting started!