Distant past are things that happened millions of years ago. Scientists know that climate was very different a long time ago and use physical evidence to find this out such as; fossilised animals, londforms and samples from ice sheets.
Ice sheets contain layers of ice and snow, within them they contain trapped carbon dioxide. Climatoligists can reconstruct past temperatures by using these ice sheets to meause the amount of carbon dioxide locked within the ice layers.
During quaternary (the last 2.6 million years of geological time), intergalcials lasted 10.000 - 15,000 years and glacials lasted 80,000 - 100,000 years.
Recent past is evidence for climate change in more recent times using evidence such as; old photographs, paintings, books, newspapers, diaries, harvests, tree blossom and migration of birds. These sources give us some udea of overall climate trends in the recent past.
Climate Change Theories:
Eruption theory - Big volcanic eruptions can change the earths climate because they produce ash and sulphur dioxide. The ash and gas form a blanket around the earth and will stop some sunlight reaching the earths surface, instead it will be reflected off the ash and gas blanket back into space. This cools the planet and lowers the average temperature.
Sunspot theory - Chinese astronomers started to record sunspots on the sun, sometimes the sun has alot of spots and at other times there are very few. These spots tell us that the sun is more active than usual. Lots of spots means there is more solar energy being produced by the sun. Cooler periods and warmer periods may have been caused by the spots.
Orbital theory - Some scientists think that the changes in the earths climate are due to the change in the way the earth orbits the sun; sometimes it goes circular-oval-circular, sometimes it goes tilt-straight-tilt and sometimes it goes wobble-straight-wobble. These alter the amount of sunlight the earth recieves.
Ecosystems and Extinction:
Plants and animals live together in ecosystems, they depend on each other and the climate and are linked together in food chains. If one part of an ecosystem changes other parts will also change so if climate changes, it can affect a whole ecosystem.
65 million years ago dinosaurs became extinct either because of a strike by a massive asteroid or a huge volcanic eruption. Both events are known to have happened menaing huge amounts of dust, ash and gas were thrown into the air blocking out the sun. Plants would have struggled to grow as the climate cooled and ecosystems would have been destroyed due to food chains collapsing.
Megafauna also had 'mass extinction' in the more recent past about 15,000 years ago. They became extinct because the climate warmed about 6*C in only 1000 years meaning many animals had to move. They migrated and tried to find new areas to live in however it was hard to find a place where the climate was suited and they had the right plants to eat. Due to all of this they became extinct.
The Greenhouse Gas Effect:
The main gases that make up the earths atmosphere are; nitrogen (78%) important for plant growth, oxygen (21%) breathed in by animals, carbon dioxide(0.03%) breathed in my plants and water vapour (1%) part of the water cycle.
There is only a small amount of carbon dioxide but is essential to regulate the earths temperature, too much makes it very hot and too little makes it very cold.
The greenhouse gases include carbond dioxide, methane, nitrous oxide and halocarbons. The extra greenhouse gases that pollute that atmosphere are produced by humans and add to the enhanced greenhouse effect. More heat is trapped in the atmosphere by greenhouse gases, increasing the earths temperature.
UK Future Climate:
Costs of a warmer climate:
- farmers will have to change crops so they need less water and more sun
- hotter weather leads to more illness like heatstroke and cancer
- there will be more droughts and water shortages in the UK
- some plant and animals won't survive in the hotter climate
Benefits of a warmer climate:
- more tourism coming in to the UK boosting the economy
- there will be fewer deaths in hypothermia
- in winter heating costs and road gritting costs will be reduced
- you can grow crops in alot more places when its hot boosting economy
Egypt's Future Climate:
Costs of a warmer climate:
- the sahara desert will spread increasing desertification
- less and more unreliable rainfall
- heatwaves bringing more illnesses and deaths
- the spread of diseases such as malaria
- falling crop yield as temperature rises and water shortages increase
- sea levels could rise by over 50cm meaning 1/3 of the city will be underwater
- 10% of the Nile Delta would flood, so over 7 million people would have to find somewhere else to live and crops would be ruined reducing food production.