The sun’s energy drives the Earth’s weather and climate and heats its surface. Some of this energy radiates back into space, but some of it is trapped by greenhouse gases (carbon dioxide, water vapor, and other gases). A natural “greenhouse effect” keeps the Earth warm enough for life to flourish, but if too much heat is trapped, the Earth’s climate could change in disruptive and dangerous ways.
There is a growing scientific consensus that increasing emissions of greenhouse gases (GHG) are affecting the Earth’s climate. That consensus is represented by the work of the Intergovernmental Panel on Climate Change (IPCC), a body established by the World Meteorological Organization and the United Nations to assess scientific, technical, and socioeconomic information relevant for the understanding of climate change, its potential impacts, and options for adaptation and mitigation.
The IPCC’s Fourth Assessment Report, released in November of 2007, states, “Warming of the climate system is unequivocal, as is now evident from observation of increases in average air and ocean temperatures, widespread melting of snow and ice, and rising global average sea level.” The report notes that eleven of the last twelve years (1995-2006) rank among the twelve warmest years of recorded temperatures (since 1850). Of concern to Florida, the IPCC report notes, “There is observational evidence of an increase in intense tropical cyclone activity in the North Atlantic since about 1970, with limited evidence of increases elsewhere.”
A key finding of the Fourth Assessment’s 123-page “Summary for Policymakers” is: “Observational evidence from all continents and most oceans shows that many natural systems are being affected by regional climate changes, particularly temperature increases.” A change from the previous report was the increased confidence in findings.
“In terrestrial ecosystems, earlier timing of spring events and poleward and upward shifts in plant and animal ranges are with very high confidence linked to recent warming. In some marine and freshwater systems, shifts in ranges and changes in algal, plankton and fish abundance are with high confidence associated with rising water temperatures, as well as related changes in ice cover, salinity, oxygen levels and circulation.”
Another finding on greenhouse gas (GHG) emissions is: “Global GHG emissions due to human activities have grown since pre-industrial times, with an increase of 70% between 1970 and 2004.” On a positive note, the Summary states: “Both bottom-up and top-down studies indicate that there is high agreement and much evidence of substantial economic potential for the mitigation of global GHG emissions over the coming decades that could offset the projected growth of global emissions or reduce emissions below current levels.” Charts and graphics in the report aid in understanding the complex scientific information presented.
In its Third Assessment Report published in 2001, the IPCC noted that the Earth’s surface temperature had increased by about 1 degree Fahrenheit in the past century due largely to increased GHGs from human activities that result in emissions of carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), halogenated fluorocarbons (HCFCs), ozone (O3), per-fluorinated carbons (PFCs), and hydrofluorocarbons (HFCs). Aerosols, including sulfate particles and black carbon (soot), are also believed to contribute to global warming. Uncertainty remains in our understanding of how the climate system varies naturally and reacts to emissions of greenhouse gases and aerosols.