The accelerating rate of global change

The Earth's surface temperature represents a balance between incoming solar energy, partial reflection (planetary albedo) and reradiation from the planet modified by the greenhouse effect of atmospheric gases having three or more atoms per molecule. Over the past 6,000 years the Earth's surface temperatures have remained remarkably stable. However during the last century it became increasingly apparent that human activities, especially the burning of fossil fuels were affecting the planet and causing global warming. The perturbation of climate brought on by humans has been recognized by the proposal of the terms Anthropocene or Anthropogene for the period since the beginning of the industrial revolution or even earlier, when CO2 levels began to rise rather than decline after the beginning of the current interglacial. There are four major greenhouse gases in Earth's lower atmospheric layer, the troposphere: water vapor, carbon dioxide, methane, and nitrous oxide. The atmospheric content of water vapor is controlled by temperature, so its distribution is restricted to the tropics and subtropics and lower part of the troposphere. Methane and nitrous oxide both have short atmospheric lifetimes of a decade or two. However, CO2 introduced into the atmosphere has a lifetime of tens of thousands of years or more. Burning of fossil fuels has increased the level of atmospheric CO2 by about 45 % over the level prior to the industrial revolution. The increasing greenhouse effect is augmented by a series of feedbacks, most positive (+), but a few negative (-), which have appeared in the climate system: Changes in (1) the thermohaline circulation system (+ or -); (2) the Atlantic to Pacific vapor transport (+); (3) Arctic river runoff (+); (4) melting of Arctic sea ice (+); (5) the ice-albedo feedback (+); (6) addition of methane from melting permafrost (+); (7) changes in the rate of ocean mixing (+); (8) changes in vegetation (+ or -); (9) wildfires (+); (10) soot accumulation on snow and ice (+); (11) accelerated melting of the Greenland Ice Sheet (+); (12) decay of the Antarctic Ice Sheet (+); (13) expansion of Southern Ocean sea ice (-), and perhaps an additional potential feedback, (14) slowing the rate of organic matter sinking into the deep ocean (+). 'Global dimming' refers to a decrease in insolation reaching the surface of the Earth as a result of introduction of aerosols into the atmosphere, resulting in pauses in the general greenhouse warming. The increasingly chaotic weather is an indication that the Earth's climate system is becoming unstable in response to the ongoing perturbation.