climate change

If humanity wishes to preserve a planet similar to that on which civilization developed and to which life on Earth is adapted, paleoclimate evidence and ongoing climate change suggest that CO2 will need to be reduced from its current 385 ppm to at most 350 ppm ... If the present overshoot of this target CO2 is not brief, there is a possibility of seeding irreversible catastrophic effects.

Two degrees Celsius is guaranteed disaster... It is equivalent to the early Pliocene epoch [between 5.5 and 2.5 million years ago] when the sea level was 25m higher. What we don't know is how long it takes ice sheets to disintegrate, but we know we'd be starting a process which then is going to be out of control. Because the way it works – the planet is out of energy balance, most of the additional energy is going into the ocean, which melts the ice shelves, which then allows the ice sheets to discharge ice more rapidly – if you want to stop that and you've pushed it up to two degrees, then you've got to cool off the ocean. Well that's going to take hundreds of years. So you would have a situation which can't be fixed except with some geo-engineering, which is a pretty awful inheritance to leave for our children....

We've reached a point where it's clear we can't burn all the coal or unconventional fossil fuels [such as oil from tar sands, deepwater drilling and sources revealed by melting ice]. We've got to phase them out. The large pools of oil and gas that are readily available to Russia, Saudi Arabia and the Middle Eastern countries is enough to get us well over 450ppm1.

• 1. In 2008 Hansen published a paper with some ten co-authors, "Target Atmospheric CO2: Where Should Humanity Aim?" which redefined our understanding of what constitutes dangerous climate change. It concluded that we need to reduce the levels of carbon dioxide in the atmosphere from 390 parts per million (ppm) to below 350

The Ecological Footprint tracks the area of biologically productive land and water required to provide the renewable resources people use, and includes the space needed for infrastructure and vegetation to absorb waste carbon dioxide (CO2). It also shows a consistent trend: one of continuous growth (Figure 2). In 2007, the most recent year for which data is available, the Footprint exceeded the Earth’s biocapacity — the area actually available to produce renewable resources and absorb CO2 — by 50 per cent. Overall, humanity’s Ecological Footprint has doubled since 1966. This growth in ecological overshoot is largely attributable to the carbon footprint, which has increased 11-fold since 1961... However, not everybody has an equal footprint and there are enormous differences between countries, particularly those at different economic levels and levels of development.

The Pentagon devours about 330,000 barrels of oil per day (a barrel has 42 gallons), more than the vast majority of the world's countries. If the U.S. military were a nation-state, it would be ranked number 37 in terms of oil consumption - ahead of the likes of the Philippines, Portugal, and Nigeria - according to the CIA Factbook.

The amount of oil consumed per soldier per day in wartime has increased by 175 percent since Vietnam, given the Pentagon's increasing use and number of motorized vehicles. A 2010 study by Deloitte, the financial services company, reports that the Pentagon uses 22 gallons of oil per day per soldier deployed in its wars, a figure that is expected to grow 1.5 percent annually though 2017.

The worst offender is the Air Force, which consumes 2.5 billion gallons of aviation fuel a year, and accounts for more than half of the Pentagon's energy use. Under normal flight conditions, a F-16 fighter jet burns up to 2,000 gallons of fuel per flight hour. The resulting detrimental impact on the Earth's climate system is much greater per mile traveled than motorized ground transport due to the height at which planes fly combined with the mixture of gases and particles they emit.