#3 This is a multistep problem, and a bit complicated, but it will lead you to y
ID: 152549 • Letter: #
Question
#3 This is a multistep problem, and a bit complicated, but it will lead you to your own roughly accurate estimate of the warming from the present level of CO2 in the atmosphere.
a) Estimate, from the above problem, how much hotter the Earth will eventually get if the level of carbon dioxide and other human-made greenhouse gases remain at the present value. You will do this by estimating the increase in temperature due to the part of the natural greenhouse effect which is attributable to CO2, and then making an extrapolation to today’s CO2 concentration. (For the warming by the natural greenhouse effect, you may use the value I calculated in class, or the value in the book.) CO2 itself produces about 20% of the natural greenhouse effect, while the majority is due to water vapor. Therefore, if humans raise the CO2 level by 5%, for example, we increase the total greenhouse effect by 20% × 5% = 1%. By what percentage have we actually increased CO2? Use this information to estimate the temperature rise that will follow. I get around 6°F. (This is an increase of about a third as much as the natural warming since the ice ages, so it’s enough to change the planet a lot. And of course the CO2 concentration isn’t staying the same, it’s growing, and at a faster and faster pace. Finally, we are producing the other greenhouse gases such as methane at alarming rates as well.)
b) Why is Venus so extremely hot? That is, why is the greenhouse effect so strong on that Planet?
(please answer both a and b, handwriting is not acceptable)
Explanation / Answer
A.The world consumes ever more fossil fuel, greenhouse gas concentrations will continue to rise, and Earth’s average surface temperature will rise with then. Based on a range of plausible emission scenarios, average surface temperatures could rise between 2°C and 6°C by the end of the 21st century.
Snow and ice
Perhaps the most well known feedback comes from melting snow and ice in the Northern Hemisphere. Warming temperatures are already melting a growing percentage of Arctic sea ice, exposing dark ocean water during the perpetual sunlight of summer. Snow cover on land is also dwindling in many areas. In the absence of snow and ice, these areas go from having bright, sunlight-reflecting surfaces that cool the planet to having dark, sunlight-absorbing surfaces that bring more energy into the Earth system and cause more warming.
Water Vapor
The largest feedback is water vapor. Water vapor is a strong greenhouse gas. In fact, because of its abundance in the atmosphere, water vapor causes about two-thirds of greenhouse warming, a key factor in keeping temperatures in the habitable range on Earth. But as temperatures warm, more water vapor evaporates from the surface into the atmosphere, where it can cause temperatures to climb further.
CLOUDS
Closely related to the water vapor feedback is the cloud feedback. Clouds cause cooling by reflecting solar energy, but they also cause warming by absorbing infrared energy (like greenhouse gases) from the surface when they are over areas that are warmer than they are.
The Carbon Cycle
Increased atmospheric carbon dioxide concentrations and warming temperatures are causing changes in the Earth’s natural carbon cycle that also can feedback on atmospheric carbon dioxide concentration. For now, primarily ocean water, and to some extent ecosystems on land, are taking up about half of our fossil fuel and biomass burning emissions. This behavior slows global warming by decreasing the rate of atmospheric carbon dioxide increase, but that trend may not continue. Warmer ocean waters will hold less dissolved carbon, leaving more in the atmosphere.
These considerations mean that people won’t immediately see the impact of reduced greenhouse gas emissions. Even if greenhouse gas concentrations stabilized today, the planet would continue to warm by about 0.6°C over the next century because of greenhouses gases already in the atmosphere.
B.Although Venus is not the planet closest to the sun, its dense atmosphere traps heat in a runaway version of the greenhouse effect that warms Earth. As a result, temperatures on Venus reach 870 degrees Fahrenheit (465 degrees Celsius), more than hot enough to melt lead.
Gases in the atmosphere such as carbon dioxide do what the roof of a greenhouse does. During the day, the Sun shines through the atmosphere. Earth's surface warms up in the sunlight. At night, Earth's surface cools, releasing the heat back into the air.
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