Answer to Question 1
ANSWER: When the rate of the incoming solar energy balances the rate of outgoing infrared energy from Earths surface and atmosphere, the Earth-atmosphere system is in a state of radiative equilibrium. Increasing concentrations of greenhouse gases can disturb this equilibrium and are, therefore, referred to as radiative forcing agents. The radiative forcing provided by extra CO2 and other greenhouse gases has increased by about 3 W/m2 over the past several hundred years, with the most rapid increase occurring over the last several decades. At the same time, increasing amounts of Sun-blocking aerosols emitted by human activity (such as sulfates and other pollutants), together with their effects on cloudiness, have led to a decrease in radiative forcing estimated at roughly 1 W/m2, which counteracts part of the greenhouse forcing.
Answer to Question 2
ANSWER: Global warming in any given year is small, and only becomes significant when averaged over many years, such as decades. So it is important not to base global warming on a specific weather event. For example, a January cold wave across eastern North America in 2014 sent temperatures plummeting. Atop Mount Mitchell in North Carolina, a low temperature of 31C (24F) was the second coldest reading ever observed there. Binghamton, New York, dipped below 0F on ten days, the most ever recorded there in January. Yet at the same time, it was the third warmest January on record in California, and globally, January 2014 was the fourth warmest on record. (Note that the United States only represents about 2 of the entire surface area of the planet, so one cannot use United States conditions alone as an index of how much the entire world is warming.)
The Greenhouse Effect
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