As ice forms, tiny bubbles of air are trapped in the ice. Each bubble is a tiny sample of air from the past; Scientists can measure how old they are from the depth they come from in the ice.
The trapped air contains a record of the carbon dioxide and methane levels at the time. This then gives an indication of what the temperature was like – the more CO2 the warmer the temperatures were.
By comparing these readings from a large number of ice cores we can have a high degree of confidence in these results.
Scientists in Cambridge have found clear evidence of a rapid increase in temperature in recent decades.
Melting ice
The world’s ice sheets are decreasing in size.
NASA data show that since 2002, the volume of ice lost in Antarctica is 134 billion tonnes per year, and 287 billion tonnes per year in Greenland.
Over the last 30 years, the Arctic ice has thinned to around half its earlier thickness.
There are fears that the Arctic could become ice-free by 2100.
Rising sea levels
Sea levels have risen by 19 centimetres since 1900 and are expected to continue to rise.
There are two reasons why sea levels have risen:
When temperatures rise and freshwater ice melts, more water flows to the seas from glaciers and ice caps
When ocean water warms it expands in volume – this is called thermal expansion
Glacial retreat
Photographs of glaciers taken in the Alps and other high mountain ranges since the mid-1800s highlight changes in the Earth’s climate.
Glaciers throughout the world are shrinking and retreating.
It is estimated that some may disappear completely by 2035.
Glaciers in Iceland are retreating at up to 50 metres a year.
Direct instrument readings
Direct measurements of temperature using thermometers show a clear warming trend.
Measurements show that, since the 1970s, there has been a rapid global temperature increase of around 0.55oC.
The warmest years on record have occurred in the last two decades with 2005 and 2010 only being beaten by the temperatures in 2014 when the average land and ocean temperatures were 0.69oC above the long-term average.
Increase in extreme weather events
No single extreme weather event can be blamed on climate change. However, scientists believe that a trend over many years could be linked to a warming world.
More energy in the atmosphere could lead to more intense storms.
The atmospheric circulation may be affected, bringing floods to normally dry regions and heatwaves to normally cooler areas.
In 2011 the IPCC concluded that extreme weather would become more common as global warming heats the planet.
Causes of climate change
Natural causes
Orbital Changes The Earth’s orbit has 3 distinct cycles, known as Milankovitch cycles:
The Earth’s orbit is sometimes circular, and sometimes more of an oval. A complete cycle from circular to oval and back to circular again occurs every 100,000 years. The cycle coincides closely with the alternating cold and warm periods in the Quaternary period.
The Earth’s axis tilts. Sometimes it is more upright, and sometimes more on its side, moving back and forth between two extremes every 41,000 years.
The Earth’s axis wobbles, like a spinning top about to fall over. A complete wobble cycle takes about 26,000 years.
These three orbital changes alter the amount of the Sun’s energy that the Earth receives. Volcanic Activity Violent volcanic eruptions produce ash and sulphur dioxide gas. If the ash and gas rise high enough, they will be spread around the Earth by high level winds. The blanket of ash and gas will stop some sunlight reaching the Earth’s surface. Instead, the sunlight is reflected off the ash and gas, back into space. This cools the planet and lowers the average temperature. In 1991, Mount Pinatubo in the Philippines erupted. This was enough to reduce global sunlight by 10%, cooling the planet by 0.5°C for about a year. Solar Output The Sun’s output (amount of energy produced) is not constant. It depends on the presence of sunspots. Sunspots are dark patches on the surface of the Sun. The number of sunspots increases from a minimum to a maximum and then back to a minimum over a period of about 11 years. This 11 year period is called the sunspot cycle. When sunspot activity is at a maximum the Sun gives off more heat. Large explosions occur on the surface of the Sun resulting in solar flares. This results in more solar energy being fired out from the Sun towards Earth. When sunspot activity is at a minimum the solar output is reduced. This can lead to lower temperatures on Earth. For example, very few sunspots were observed between the years 1645 and 1715. This coincided with the coldest period during the ‘Little Ice Age’ when Europe experienced a much colder climate with severe winters.
Human causes
Use of Fossil Fuels When fossil fuels (coal, oil and natural gas) are burned - by industry, in power stations and by vehicles and planes – gases enter the atmosphere. Carbon dioxide (CO2), in particular, is given off when fossil fuels are burned. Fossil fuels account for the majority of global greenhouse gas emissions – over 50%. Although these gases have always been present in the world's atmosphere, their concentration is gradually increasing as more and more fossil fuels are burned. Scientists believe that the build-up of so-called greenhouse gases in the atmosphere acts like a blanket or greenhouse around the planet; heat is trapped inside the Earth's atmosphere. This is the greenhouse effect, and the resulting increase in global temperatures is called global warming. As the world’s population grows and wealth increases, people are demanding more and more energy, which increases the use of fossil fuels and the release of carbon dioxide.
Agriculture Agriculture produces large volumes of methane and contributes to approximately 20% of global greenhouse gas emissions. For example:
cattle (cows) produce methane during digestion;
rice farming - microbes produce methane as they decay organic matter under the water of flooded rice paddy fields.
As the world’s population increases, more food is required, especially in areas such as Asia where rice is the staple diet. This means the demand for meat and rice is higher and methane levels are rising. If current population rates continue, it is inevitable that large-scale agriculture’s contribution to climate change will continue to grow.
Deforestation Deforestation is the clearing of forests on a huge scale. If deforestation continues at the current rate, the world’s forests could disappear completely within a hundred years. There are several reasons why forests are cut down:
logging for wood and paper products;
making room for the expansion of urban areas;
clearing land for agriculture (space for crops and livestock);
building roads to access remote areas.
During the process of photosynthesis, trees absorb carbon dioxide, which reduces the amount of carbon dioxide in the atmosphere. Deforestation leaves fewer trees to absorb carbon dioxide. Therefore the enhanced greenhouse gases contribute to rapid climate change. In addition, when trees are burnt to clear an area, such as with slash and burn, the carbon dioxide that has been stored is also released, which again contributes to climate change.
Mitigation is action taken to reduce or eliminate the long-term risk to human life and property from natural hazards, such as building earthquake-proof buildings or making international agreements about carbon reduction targets.
Adaptations is actions taken to adjust to natural events such as climate change, to reduce potential damage, limit the impacts, take advantage of opportunities, or cope with the consequences.
Adaptation 1 - Change in agricultural systems Agriculture (farming) will need to adjust to climate change. In particular, it will need to adapt to changing temperature and rainfall patterns and an increase in extreme weather events such as heatwaves, droughts and flooding. To adjust farmers and governments will need to consider:
Changing the crops and varieties grown, e.g. introducing drought-resistant crops such as wheat variety Seri M82 with a deeper root system to help access more water.
Changing the time of year crops are planted.
Educating farmers on how to use technology (e.g. dams and reservoirs) to “harvest” water in areas where rainfall decreases.
Educating farmers on how to conserve soil moisture in areas where rainfall decreases.
Planting shade trees to protect seedlings from strong sunshine in areas where temperature increases.
Moving crop production to new, more suitable, locations.
Draining water to prevent water logging, erosion, and nutrient leaching where rainfall increases.
Changing livestock breeding practices and shifting grazing patterns.
Improving pest, disease, and weed control as these might change location with climate change.
The cost of adapting to climate change will be more difficult for poorer subsistence farmers. Importance: If we are to feed the world, the United Nation’s Food and Agriculture Organisation says that agriculture will need to be ‘climate smart’.
Adaptation 2- Managing water supply Dry areas are predicted to get drier, leading to more water shortages. There are two ways water can be managed:
Reducing Demand – In London, a Water Strategy is being used to reduce water demand. By 2030, all London homes are to be offered a free package of water-saving devices such as tap aerators and shower timers.
Increasing Supply – Thames Water opened a desalination plant in London in 2010 to increase water supply. Water is taken from the River Thames at low tide (when it is least salty) and turned into drinking water for 400,000 homes.
An artificial glacier project is being used in the Himalayas to supply water to villages in Ladakh, India. Water is collected in winter and frozen as an artificial glacier. When the ‘glacier’ melts in spring it provides water for the local villages. Adaptation 3 - Reducing risk from rising sea levels Sea levels are predicted to rise by up to 82cm by 2100, which would flood many islands and coastal areas. Managing rising sea levels in the Maldives: Background Information: The Maldives are a group of islands in the Indian Ocean. The highest point on the islands is just 2.4 metres above sea level. Some climate models suggest the islands may be uninhabitable by 2030 and completely submerged by 2070. Adaptations – How can the Maldives manage sea level rise?
A 3 meter sea wall is being constructed around the capital Male with sandbags used elsewhere.
Houses are being built that are raised off the ground on stilts
Coastal mangrove forests are being replanted – the tangled roots of the trees trap sediment and protect the coastline from storm waves.
The entire population could be relocated to Sri Lanka or India
Artificial islands could be constructed to relocate people to.
Managing rising sea levels in London: London is currently well protected against sea levels. The Thames Barrier was built in 1982 to stop tidal surges (sea water) entering central London. It has been closed over 100 times since it was built, preventing central London from flooding. As sea levels rise, it is likely that the Thames Barrier will need to be closed more frequently.
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