Greenhouse gases and climate change

what are greenhouse gases

gases found in the atmosphere, including carbon dioxide, methane and water vapour, which are involved in the greenhouse effect

what do greenhouse gases do?

• Greenhouse gases reduce the amount of heat lost from the surface of the earth. This is similar to the effect of a green house where the glass panels will reduce heat lost.

• Without the greenhouse gases earth would likely be -63 degrees average temperature and this would not be suitable for sustaining life on earth.

what is greenhouse effect?

the process by which gases in the Earth’s atmosphere absorb and re-radiate the radiation from the Sun, which has been reflected from the Earth’s surface, maintaining a temperature at the surface of the Earth that is warm enough for life to exist

explain role fo greenhosue gases in climate change

• When radiation from the sun reaches the earth, some is reflected back into space by atmosphere and some is absorbed by the atmosphere.

• Greenhouse gases accumulate /increase in teh upper atmosphere

• They allow UV/short wavelength/ visible light through/to reach earths surface

• The earth then emits long wave infrared radiation.

• Greenhouse gases prevent the exit of/trap/absorb IR radiation/ long wavelength light and re radiate it causing the atmosphere and surface of the earth to increase in temperature.

what is global warming?

• Global warming is the increase of temperature in the earths atmosphere or on surface of the earth. Global warming and global cooling have occurred many times in the history of Earth.

• The greenhouse effect is important to ensure that Earth is warm enough for life; if it were not for the insulating effect of greenhouse gases, Earth would see similar dramatic temperature fluctuations to its neighbouring planets

  • Temperatures on Mars range between 20°C and −153°C

what is climate

• Climate is the average weather in a large area (country/continent) over a long period of time. Measurements taken and considered when deciding climate are – mean temperature, precipitation, wind, humidity and atmospheric pressure over a period of time.

• The time climate is measured over is a period of 30 years.

what is weather?

• Weather is the conditions of the atmosphere at any

particular time. Sunny, windy, rainy. Weather forecasts

describe the weather on any particular day.

• Weather can vary day to day but climate is expected to be

stable over time.

how weather can be linked to climate change

Extreme weather events include cyclones, longer sever

droughts, violent storms and flooding. These events have

been increasing in frequency. There is evidence this increase

is linked to climate change.

what is climate change

• a large-scale change in global or regional weather patterns over a period of many years

how climate change is occurring

• E.g. average temperature at earths surface is 14 degrees for 11000 years but it has increased 0.89 degrees between 1901 and 2012. This is a very rapid change. Rainfall also changing over time. However it is difficult to measure and draw conclusions as climate change occurs over long periods of time.

• A single unusually hot year does not count as climate change but if average temperature and average rainfall changes the same way over many years then this indicates climate change may be occurring.

what are the greenhouse gases

many including

• Carbon dioxide

• methane

• water vapour

• nitrogen oxides

• CFCs

what is anthropogenic climate change?

changes to weather patterns/global temperatures over a long period of time due to human activity

why carbon dioxide levels have been fluctuating

• Atmospheric carbon dioxide levels have fluctuated throughout Earth's history due to events such as volcanic eruptions and the weathering of limestone rocks

• Since the industrial revolution, however, atmospheric carbon dioxide levels have risen to their highest in Earth's history

• The industrial revolution began in the late 1700s when the combustion of fossil fuels to power factories, transport, and homes became commonplace

  • Fossil fuel combustion releases carbon dioxide

• A clear correlation can be seen between increasing levels of carbon dioxide since the industrial revolution and increasing global temperatures, providing evidence for the role of human activities in causing global warming. However correlation doesn’t prove causation.

how is carbon dioxide released

• In addition to the burning of fossil fuels, carbon dioxide is also released into the atmosphere when natural carbon sinks are damaged or destroyed by human activities

  • Carbon sinks include trees, soils, peat bogs, and the oceans

    • Deforestation, soil degradation, peat harvesting, and ocean warming all contribute to the addition of carbon dioxide to the atmosphere

what is methane

• Methane is a simple hydrocarbon and it has contributed to global warming about 72 x more than more than carbon dioxide in the last 20 years.

• It is present as a gas in the atmosphere, and underground, and is the main component of natural gas fossil fuel

• Less methane is produced than carbon dioxide.

• It is produced from decay of organic matter by some types of bacteria and from digestive systems of ruminant such as deer and cows.

how levels of methane have increased due to humans?

• Methane risen by 150% since 1750

• Methane can be produced by several human activities

  • Methane is released from the guts of ruminant mammals such as cattle

    • While this is clearly not a direct human activity(!) the intensive farming of such animals has greatly increased their contribution to atmospheric methane

  • Landfill sites release methane when organic matter such as food waste decomposes

  • Extraction of fossil fuels from underground releases methane

  • Anaerobic bacteria in waterlogged rice paddy fields release methane

• the warming of the poles that results from global warming also leads to the release of methane from natural stores such as permafrost

  • Permafrost is ground that remains frozen all year round

what is correlation

a strong tendency for two sets of data to vary together

CO2 levels and ocean acidity

• Carbon dioxide levels are 40% higher than pre industrial times.

• This is a result of burning fossil fuels and deforestation. Oceans have absorbed 30% of emitted anthropogenic (produced by people) carbon dioxide. This has caused increase in ocean acidity.

is there correlation btw increase in green house gases and global temperatures?

• Many studies suggest a clear correlation between increase in carbon dioxide levels and other green house gases and increase global temperatures.

• However the correlation is so close that it is difficult to tell if increased carbon dioxide is causing increased temperature or as a result of it.

what is causal relationship?

One event happens as a direct result of another, with a clear mechanism by which one factor causes a given change

Is relationship between greenhouse gases and global warming causal?

• If the relationship is causal then we need a way of explaining how one factor changes the other. There is a clear way in which greenhouse gases raise surface temperature on Earth Through reradiation.

• We understand the natural green house effect and it is logical to consider that humans are responsible for increase In carbon dioxide levels in the atmosphere and then the mechanism for increase in global temperatures because timing of both changes is so closely linked

Evidence against the statement that humans responsible for global warming

• some scientists have said global warming is a result of events o the surface of the sun

• They suggest there is evidence that solar activity affects cloud formation and therefore surface temperature

• When considering the evidence the IPCC has deduced that sunspot and sunflare activities over the past 50 years would have led to global cooling not global warming.

• They concluded that these factors have a small implication for global climate

Why impossible to prove a causal relationship between humans releasing more greenhouse gases and climate change?

• All theories about global warming and climate change are based on data that needs interpretation.

• This uses complex computer modelling systems. However it is impossible to prove a causal link. We cannot conduct valid experiments on the atmosphere of the planer.

• A wide variety of computer models suggest the same thing that increased carbon dioxide in the atmosphere is increasing surface temperature and human carbon dioxide emissions are responsible for some of the current warming

IPCC study that humans resulted in build of greenhouse gases

• In 2007 the IPCC looked at data models of climate change and they saw that anthropogenic carbon dioxide levels have increased by 80% between 1970-2004 and this was mainly due to fossil fuel combustion emissions.

• IPCC decided that the balance of evidence showed a 95% probability that human activities have resulted in the build up of green house gases and these are at least partly responsible for the increase in global temperatures

• In 2013 the report stated that it is extremely likely that human activities are the dominant cause of global increases in temperatures.

• IPCC use language to indicate how the evidence backs up the hypothesis. They decided it is very likely that human activity have contributed to rise in sea level but only likely that these activities have contributed to the change in weather patterns

Is global warming caused by anthropogenic change only?

• They believe there is siginificant evidence that there is a causal link between anthropogenic green house gas and global warming. It is likely to be multifactorial but anthropogenic greenhouse gas emissions play a significant role