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Climate Change Update

by: Paul Kando

With the political theatrics of government shutdown monopolizing the news, serious discussion of the Inter-governmental Panel on Climate Change's (IPCC) 2013 report, released just weeks ago, has been minimal. Yet, for our children's and grandchildren's future, this report's conclusions are far more consequential than any government shutdown. Here I summarize the main consensus findings of over a thousand leading scientists from the world's academies of science and prestigious research institutions.

The climate system has warmed. There is no scientific disagreement about this. Many of the changes observed since the 1950s are unprecedented. Compared to past millennia, atmosphere and ocean are warmer, snow and ice have diminished, sea level has risen, and concentrations of greenhouse gases have increased. Each of the last three decades has been successively warmer at the Earth's surface than any preceding decade since 1850. In the Northern Hemisphere 1983-2012 was the warmest 30-year period in 1,400 years.

Over 90% of the energy accumulated in Earth's climate system since 1971 has been stored in warming ocean waters, especially the upper 700 meter (2,300 foot) ocean layer. Over the last two decades, the Greenland and Antarctic ice sheets have been losing mass, glaciers have continued to shrink, and Northern Hemisphere spring snow cover has continued to decrease. The rate of sea level rise since the mid-19th century has been greater than the mean rate during the previous two millennia. Between 1901 and 2010, the global mean sea level rose by 0.19 meters (7½ inches).

Atmospheric concentrations of carbon dioxide (CO2), methane, and nitrous oxide have reached levels unprecedented in at least 800,000 years. CO2 concentrations have increased 40% since pre-industrial times, primarily due to fossil fuel emissions and land use changes. The ocean has absorbed about 30% of the emitted anthropogenic CO2, causing acidification, with dire implications for sea life. Since 1750 the largest contribution to positive radiative forcing - the difference between radiant energy received by Earth and energy radiated back to space - comes from the increase in the atmospheric concentration of CO2.

Human influence on the climate system is evident from increasing atmospheric greenhouse gas concentrations, positive radiative forcing, observed warming, and understanding of the climate system. Improved climate models reproduce observed continental-scale surface temperature patterns and trends over many decades, including the more rapid warming since the mid-20th century and the cooling immediately following large volcanic eruptions. Model studies and observed changes in temperature, climate feedbacks, and changes in Earth's energy budget together define the magnitude of global warming in response to past and future radiative forcing. There is growing evidence of human-caused warming of atmosphere and ocean, changes in the global water cycle, reductions in snow and ice, sea level rise, and changes in climate extremes. Human influence has been the dominant cause of the observed warming since the mid-20th century. Continued emissions of greenhouse gases will cause further warming and changes in the climate system. Limiting climate change will require substantial and sustained reductions of greenhouse gas emissions.

The global surface temperature increase by the end of this century is likely to exceed 2°C (about 4°F) above the 1850-1900 mean. Warming will continue beyond 2100. It may vary from year to year, decade to decade and will not be regionally uniform. Changes in the global water cycle in response to the warming will vary as well. The contrast in precipitation between wet and dry regions and wet and dry seasons will increase, subject to regional exceptions. Oceans will continue to warm. Heat will penetrate from the surface to the deeper ocean, affecting ocean currents.

As global mean surface temperature rises, the Arctic sea ice cover will continue to shrink and thin, and Northern Hemisphere spring snow cover will decrease. Global glacier volume will further decrease, reducing summer river flows, exacerbating freshwater shortages. The global mean sea level will continue to rise at a rate greater than that observed between 1971 and 2010, due to increased ocean warming and loss of melt-water from glaciers and ice sheets. Climate change will affect Earth's carbon cycle, further increasing CO2 accumulation in the atmosphere and, as more CO2 is dissolved, ocean acidification.

Cumulative emissions of CO2 will largely determine global mean surface warming by the late 21st century and beyond. Most aspects of climate change will persist for many centuries even if emissions of CO2 are stopped. Exceeding a 2°C global temperature rise, generally considered the limit above which irreversible changes in the climate become inevitable, is a worrisome prospect, given that atmospheric CO2 concentrations have reached above 400 parts per million (ppm) for the first time in 3 million years, exceeding the widely considered "safe" maximum of 350 ppm. Limiting the warming to less than 2°C will require cumulative CO2 emissions from all anthropogenic sources to remain below 1,000 Gigatons of Carbon (GtC). Of this 531 GtC, has been already emitted as of 2011.

All this is bad news for our descendants' future. Denial is not the answer. For the sake of our children and their children, we must stop using fossil fuels. The best place to start is in our houses - over 40% of fossil fuels used currently heat buildings. We know how to dramatically reduce that amount.

As for the superbly financed climate change deniers among us, ask but one question: who benefits?