Global warming is a fact, but scientists have come up with many explanations as to why this may be. Some suggest that natural causes are to blame for climate change, proposing ideas such as the Milankovitch Theory. This is the theory that variations in the Earth’s orbit around the sun such as a stretch, tilt or wobble of the axis lead to changes in the amount and distribution of solar radiation received by the Earth from the sun. The fact is that although this theory supports ideas of ice ages and warmer inter-glacials, these cycles occur over tens of thousands of years, and only changes the temperature by 0.5°c which does not add up to the rapid climate change that we are experiencing today or the ice ages which were at least 5° c cooler. Other theories that scientists have proposed include sunspots which are variations in solar output, making darker areas of the sun have an increased output on an 11 year cycle, and also the impacts volcanic eruptions releasing particles into the atmosphere that absorb infrared radiation, heating up the earth’s surface. However, again flaws have been found in these findings as a 2006 study showed that no net increase in solar output activity has occurred since the mid-1970s, and volcanic eruptions are rare and usually only have short term effect of 2-3 years. As a result, many scientists find that although natural factors may contribute to climate change, the rapid increase that the world is currently experiencing cannot be explained by them alone. No know natural factor can account for the warming of the last 50 years. IPCC scientists believe external forcing by anthropological factors therefore must also come into play.
Climate is affected mostly by two human activities; the enhanced greenhouse gas emissions and the destruction of the world’s natural CO2 sinks. The enhanced greenhouse effect is an extreme version of the earth’s natural greenhouse effect. Through this process, some of the sunlight that hits the earth is reflected back into space and some is reflected by the natural gasses (CO2, water vapour, methane etc.) that surround the earth back to the planet itself, having a warming effect. Without this greenhouse effect, the earth’s temperature would decrease by about 18°c and so this process is vital in the maintenance of our planet’s delicate environment. The enhanced greenhouse effect however is the increase in the effectiveness of the process due to an increase in the quantity of greenhouse gases in the atmosphere caused by human activities. This causes the gasses to reflect more of the sun’s rays back to earth as the layer of gasses is thicker, heating the earth further. There is evidence to show that the increase in greenhouse gasses has occurred since 1750, marking it simultaneously with the commencing of the Industrial Revolution. This would make sense as it was with the Industrial Revolution that the world saw the large scale burning of fossil fuels to provide energy for industrial activities. Since the 1980’s, 75% of CO2 emissions have come from the burning of fossil fuels as they supply most of the energy needed to run vehicles and generate electricity for industries and households. Pre-industrial levels of carbon dioxide were about 280 parts per million, and current levels are greater than 380 ppm, increasing at a rate of 1.9 ppm a year since 2000. The global concentration of CO2 in our atmosphere today also far exceeds the natural range over the last 650,000 years of 180 to 300 ppm. The correlation between C02 output and temperature change marks a unquestionable link, that increases in CO2 levels have impacted on the climate. Interestingly, this correlation also extends to population trends, as this follows a similar pattern. This would suggest that as populations increase, the demand for energy also increases, heightening the levels of CO2 emitted and therefore increasing the rate of global warming. Rapidly developing countries such as China and India intensify this demand for electricity, as both of these countries have huge populations and as they are rapidly urbanising, demand for electricity, building materials, water and other natural resources are all on the increase. They also play a huge factor in providing other countries with goods as they manufacture goods on huge scales, again increasing their energy needs. To feed such a large population you need much food, the response to which is growing large fields of paddy rice and cheap meat production contribute greatly to methane emissions.
The other great contributor to climate change is the destruction of the earth’s natural CO2 sinks. One example of a sink is the ocean, as CO2 dissolves in seawater naturally and gets moved to the deep ocean by ocean currents and much of this CO2 is stored in ice. However, as the earth’s temperature increases ice caps in the Polar Regions are melting, releasing more CO2 into the atmosphere. NASA satellite data shows that floating arctic sea ice is declining by 8.5% per decade, along with the melting of the Greenland ice sheet which has increased by 16%. At this rate, 50-60% of Arctic ice could be lost by 2100. Approximately 1/3 of human generated emissions are stored in oceans, so with the melting of this ice a huge amount of CO2 is released into the atmosphere. Another example of a sink is plants, as they convert CO2 into organic matter and oxygen through photosynthesis, and are vital in maintaining the balance of gasses in the environment. Rainforests every year help to absorb almost 20% of manmade CO2 emissions; therefore deforestation can be classes as a major contributor to the causes of climate change. Cutting down rainforests faster than they can be replaced has a devastating effect on the carbon emission cycle, producing an extra 17% of greenhouse gasses. Agriculture has also been shown to produce significant effects on climate change, primarily through the production and release of carbon dioxide, methane and nitrous oxides which contribute to the greenhouse effect. Also, when agriculture alters the Earth’s land cover, it can change its ability to absorb or reflect heat and light.
Land use change such as deforestation and desertification, together with the use of fossil fuels are the major anthropogenic sources of carbon dioxide. It is impossible to say however that these reasons are solely to blame for climate change, as there may be other factors that are unknown to us currently, and different scientists have different view to the extent that each factor contributes to this effect.
by
jasminetrixie101 (student)
