What is the greenhouse effect and how does it warm the earth?
The sun generates and projects vast amounts of energy, right across the frequencies that make up the electromagnetic spectrum. What that means is that the sun’s energy is transmitted through wavelengths of different frequencies. The sun’s peak intensity is emitted as visible light. Just below visible light in the electromagnetic spectrum is infrared radiation, and the next frequency up is ultraviolet.
Some of the sun’s energy is reflected back in to space; a 1/3 in fact. It bounces off the atmosphere directly, and some if reflected back off the earth’s surface (land, ocean, and ice) – this is why you can ‘see’ the earth from space, it is the surface reflecting visible light; what we can’t ‘see’ is the energy which is bouncing back at other electromagnetic frequencies. This leaves 2/3 of the sun’s energy which is absorbed by the Earth, especially the ocean (much more of that later). This heats up the planet. The earth radiates this energy back through heat in the infrared electromagnetic frequency. Some naturally occurring gases (quite common ones such as water (H20), methane (CH4) and carbon dioxide (CO2)) allow visible light frequencies to escape back into space, but absorb and trap infrared frequencies. This means that heat does not escape and accumulates. These gases act like a blanket for the earth and keeps a much as 15.5C warmer than it would normally be if all infrared energy would radiate back into space. This process enable life as we know it.
However, the more of these gases are present in the atmosphere, the more heat is being trapped and accumulated, which increases the temperature on the earth (in the same way that if you sleep under a thicker duvet you are warmer in bed, since more of your body heat trapped under the duvet). And human activity is causing quite a lot of extra CO2 to be emitted into the atmosphere, and there this is accelerating; emissions have increase 6-fold since 1950. 250 years ago there 280 part per million CO2 in the atmosphere, now we’re gone past 400 ppm. The temperature of the earth has warmed by 0.85C since 1900, but most of that has occurred in the last 50 year (since 1970).
What is global warming? What is its relationship with naturally occurring and human-enhanced greenhouse effect?
Scientists across the globe agree on the fact the earth is warming. This consensus was enshrined in the 4th Assessment Report (2007) from the UN intergovernmental panel on climate change (IPCC), which summarized thousands of scientific studies and millions of observations. The report was approved line-by-line by each government taking part in the IPCC. The report concluded that warming “is unequivocal, as is now evident from observations of increases in global average air and ocean temperatures, widespread melting of snow and ice, and rising global average sea level.” This was again reviewed in 2010, which reflected that the report’s theories and conclusions had been tested so thoroughly that the possibility of them being wrong was extremely unlikely, i.e. climate change is a settled fact.
The existence of climate change is backed up by scientific observations; we have been breaking heat records year on year and decade on decade; as ocean warm more water evaporates causing greater humidity which has been measured; springs are occurring earlier and wildlife is noticeable adapting. The scientific model show that with rising temperature the intensity and frequency of heatwave also increased, as well as many other weather events which we will discuss in more depth.
If we agree that global warming is a settled fact, the fact the humans are causing all of it is backed up by the science. Estimates of how much warming human activity would generate, match what is being observed; i.e. there does not seem to be any other external factors. Moreover, without human activity the planets would have cooled somewhat in recent (geological) times due to low solar activity levels, volcanic activities throwing up air-born particles, and the earth’s natural orbit resulting in very slow (yet steady) cooling rates.
Scientist are as sure about the fact that humans are the primary cause of global warming, as they are sure that cigarette cause cancer (97% of publishing scientist agree). And no one has proposed a model that explains; (1) why human activity does not result in global warming while at the same time (2) finding another reasonable explanation for the amount of warming we are witnessing.
What are the main contributors to sea level rise?
One of the most noticeable, dangerous and devastating effect of global warming is sea level rise (in the last century the sea level have increased by several inches, and since 1990 the sea is rising by 0.3 centimeter a year). Crucially, some of the contributors to sea level rise are accelerating.
There are 5 key contributors to see level rise: (1) thermal expansion; when a body heats up it expands (this has contributed to half of the sea level rise in the past century), (2) depletion of ground water storage which is increasingly used for farming and drinking and thus runs off into the sea, (3) glacier ice loss (which runs off into the sea), (4) Greenland ice loss (if Greenland completely melts, sea levels would rise by 20 feet), (5) Antarctic ice Loss, which contains 90% of the world’s ice and would cause the sea levels to rise by 200 feet is it completely melted. The West Antarctic Ice Sheet (WAIS) is unstable since the ice is anchored below sea level, and so it melting from bellow (two studies in 2014 found that WAIS collapse was past tipping point).
The human-caused warming trapped by the greenhouse gas effect gets trapped either in the ocean, in the lands or in the atmosphere. However, water is extremely efficient at storing heat which mean that over 90% of human-cause warming is stored in the oceans. The temperature of oceans is measure through an global network of buoys (bathythermographs) and it is rising.