The causes of climate change can be divided into naturally occurring causes and human causes. Natural causes include the naturally occurring forces that influence the Earth, these include; Milankovitch cycles, solar variation, and volcanism. The human impact on the changing climate is usually discussed in relation to the period since the Industrial Revolution, which is when human innovation and impact began to accelerate. The impact of climate change varies across the planet, with some regions experiencing far worse threats than others.
There are three different Milankovitch cycles which describe the orbital variations in the rotation of the Earth; eccentricity, precession, and axial tilt. Together, these cycles determine the amount of solar radiation each part of the world receives. Eccentricity is the shape of the Earth's orbit around the sun. This ranges from nearly circular to elliptical and is caused by the gravitational pull of the other planets. A complete cycle of circular to elliptical and back to circular lasts 100,000 years. When the orbit is elliptical, winters are colder and summers are warmer. Because the earth is not a perfect sphere, it wobbles on its axis, similar to a spinning top. This wobble is called precession and the Earth completes this cycle in 26,000 years. This cycle is caused by the gravitational pull of the moon. Seasons are impacted by this; summers can become warmer. Axial Tilt is the angle at which the Earth's axis is pointed. This varies between approximately 21 degrees and 24 degrees over 41,000 years. A greater degree of tilt results in the Earth having a higher average temperature.
The output of the sun can be measured by monitoring sunspots on the sun's surface, these are caused by magnetic activity on the sun. Since the 1970's, a decrease can be seen in the output of the sun, meaning that the sun is not a cause for the current warming of the climate. There was a reduction in sun spots recorded during the period of the "Little Ice Age", explaining the cooling at this time.
Volcanic eruptions can result in an altered climate. Volcanoes can erupt large amounts of sulfur dioxide, which when mixed with water vapour, becomes a volcanic aerosol. This reflects sunlight away from the atmosphere and reduces the amount of solar radiation the Earth receives. Although the carbon dioxide erupted from a volcano contributes to the greenhouse effect, the effect of the sulfur dioxide is often greater, meaning that the Earth will experience cooling. The effect of sulfur dioxide will decrease over time with rainfall.
The burning of fossil fuels releases carbon dioxide and contributed to the greenhouse affect and is one of humans' main contributions to climate change. Fossil fuels are used in almost every aspect of our lives, from transport to food. As world population grows, more fossil fuels are being burned, which is adding to the warming effect. Agriculture in particular releases huge amounts of carbon dioxide, but also huge amounts of methane gas into the atmosphere. Methane has a much stronger greenhouse effect than carbon dioxide.
Agriculture accounts for about 20% of the greenhouse gas emissions in the world. As the world's population dramatically increases, food production needs to increase also. Countries in Asia in particular are experiencing a growth in the demand for rice, which is very intensive to farm and causes a lot of emissions. When countries increase their standard of living, there is an increased demand for meat production. Cattle farming is the biggest source of methane gas emissions and continues to grow as an industry. Cattle represent 1/3 of farming emissions.
Deforestation is the clearing of forested areas for timber production and to create space for other industries such as mining, agriculture, and manufacturing. The process of removing forest ecosystems itself causes emissions of greenhouse gas; but it also stops the process of photosynthesis, which is responsible for removing carbon dioxide from the atmosphere. The slash and burn method of deforestation emits huge amounts of carbon into the atmosphere as it releases the stored carbon dioxide from within the plants.
The world's glaciers are beginning to retreat. Up to 90% of the glaciers in Antarctica are facing destruction in the coming years. The melting of the glaciers at the poles will cause a shift in current ocean currents, which will affect global temperatures. It is believed that the melting of Northern glaciers will cause the gulf stream to migrate south. This could cause dramatic cooling in the UK.
The global mean sea level has risen by 10-20cm in the past 100 years. It is estimated that this adds up to 3mm per year since the 1990's. Predicting this change into the future is difficult and it is unknown how much of an impact this process will have. If sea level were to rise by 1 meter, many major cities such as New York would be underwater. The melting of the Greenland ice sheet would cause sea level to rise by up to 7 meters, which would cause cities like London to be lost also. This could lead to huge devastation worldwide.
Countries closest to the equator are likely to suffer the worst impacts of climate change. Crop yields will decrease; it is estimated that in India there will be a 50% reduction in the amount of land that can be used for agriculture. This will be lost due to hotter and drier weather. Countries which experience drought will face longer periods of drought, hotter conditions, and shorter growing seasons.
In Europe, there will be an increased number of heat waves which may lead to more deaths. However, deaths caused by colder temperatures will decrease. In Southern and Eastern Africa will experience hotter and more humid conditions, leading to a rise in malaria. An increase in natural disasters is also predicted, this will cause an increase in deaths. Food scarcity will continue to grow; hunger and famine will become more widespread.
As conditions become more extreme, it will become more difficult for species to survive. Changes in ocean temperature will cause a shift in aquatic wildlife. Habitat destruction will become widespread and species will become extinct. Eastern Amazonia, an area of tropical rainforest, may become a savannah with warmer temperatures and less water availability. Food shortages may be common for many species.