This writing attempts to concisely explain how humans are contributing to climate change and the potential ramifications and options.
The Earth’s climate is the result of very complex interactions between a myriad of physical, chemical, and electromagnetic phenomena, including sun activity, continental drift, ocean currents, atmospheric composition and currents, vegetation, volcanic activity, earth's varying orbit around the sun, etc. Study of fossil and ice core records tells us that the earth has undergone major changes in its climate in the past, and major changes will likely occur in the future. The record indicates some cyclical patterns to climate change, including a cycle of global warming and cooling, the latter resulting in “ice ages”. Except for rare catastrophic events such as a large asteroid colliding with Earth or a super volcano explosion, the Earth’s climate has changed very gradually in the past. For example, it has taken thousands of years of very gradual cooling to produce an ice age and thousands of years of very gradual warming to end an ice age.
Since the start of the industrial revolution, the amount of carbon dioxide in the atmosphere has been increasing at an ever-increasing rate, and is now changing much more rapidly than can be explained by the normal cycles. The Earth’s average global temperature has increased in a similar pattern over that time. The consensus of mainstream scientific opinion is that increasing CO2 in the atmosphere causes a temperature rise by a greenhouse effect, and that human activity is the primary cause of this increasing CO2 level (http://www.aip.org/history/climate/summary.htm,http://en.wikipedia.org/wiki/Scientific_opinion_on_climate_change). Modern humans release carbon dioxide into the atmosphere by several means, especially by burning fossil fuels. Meanwhile, the clearing of forests has reduced the rate of re-capture of CO2 by the Earth’s vegetation.
The fact that the CO2 levels and Earth’s average temperature and sea level are currently rising rapidly and unexpectedly (based on the gradual background rate of change) is not in doubt (http://www.epa.gov/climatechange/science/recenttc.html). They are continuously measured by instruments and well documented. At present, the average global temperature is increasing at a rapid rate and the Earth’s store of ice (e.g., at the poles and in high glaciers) is melting rapidly (http://en.wikipedia.org/wiki/Retreat_of_glaciers_since_1850). Scientists attempt to model the Earth’s natural systems to predict future increases in temperature and ice melt, but such models are not accurate. The most recent measurements indicate that such models have underestimated the amount of temperature increase and ice melt.
Scientists are also unable to accurately predict the resulting climate change and impacts on Earth’s flora and fauna, including humans. It is likely, but not certain, that rising temperatures will result in a much greater release of CO2 from methane release from melting permafrost. Melting ice can also result in less reflection of the sun from polar regions and therefore more warming of oceans from direct solar radiation. There are numerous potential mechanisms for rapid change, some of which cancel each other and some that reinforce each other. Some may result in higher local temperatures at some times of the year in some locations while others may result in lower local temperatures. Secondary effects on climate may include more or less rainfall or snowfall at some locations, more or fewer violent storms at some locations, more or less day-to-day wind at some locations, etc. We just don’t know.
How much will the sea level rise? How will climate change where I live and how rapidly? What animals and plants will be helped or hurt? How many humans will have to be relocated at what cost? What will be the impact on agriculture and what will be the overall economic impact? We are already observing some directly measurable effects including the demise of polar bears, certain penguins, and other ice-dependent animals and plants. But in general, we just don’t know what is in store.
We know that we and the animals and plants can continue to live very well if climate does not significantly change - it has not changed significantly over the past few thousand years. But the current rapid rate of warming is predicted to result in a similarly rapid, or more rapid, rate of change in climate and associated environmental conditions - a rate of change that does not give any living thing time to adapt via evolution.
We can continue our current practices and hope that the impact of human-caused climate change will not be too great. Or we can change our practices to drastically reduce our impacts, especially CO2 emissions and deforestation. The cost of doing the latter may be less than the former, and it has other benefits including reduced air pollution and associated health risks, and reduced international strife due to competition for limited oil resources.
But perhaps the most compelling reason to change our ways is to simply avoid that rolling of the dice. We may get lucky (climate changes may turn out to be mild and have only small negative impacts) but we may get very unlucky. Changing our practices seems like a prudent insurance policy, given what is at stake.
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