Climate: Past, Present, Future [Prof John McClatchey]Presentation Transcript
Climate: Past, Present, Future
UHI Millennium Institute: Environmental Research Institute
The aim of this presentation is to give an overview of:
What controls the climate?
What do we know about global climate in the past?
Why does climate change?
Climate in the UK and Scotland
How do we make predictions about future climate?
What global changes are expected?
What changes are expected in Scotland?
The Climate is a result of the Energy Balance of the Earth Source: IPCC (2007) Outgoing longwave (infra-red) radiation from the surface is absorbed by atmospheric gases and clouds and re-emitted back to the surface. This is called the “greenhouse effect” (but greenhouses work differently) and without it the temperature would be about 33 deg C colder
Climate in the past 450,000 years We can estimate the climate of the past using ice cores from the Antarctic and Greenland Ice sheets. Ice cores are analysed to provide an estimate of past temperatures and both the Greenland and Antarctic cores show there have been a series of Ice Ages and Interglacials. In an Ice Age the average global temperature is about 5 o C cooler than at present. The temperatures from the Vostok ice core are shown on the next slide. Vostok is a Russian research station in the Antarctic where the average annual temperature at is -55 o C and temperatures as low as -89 o C have been observed.
Climate in the past Adapted from Petit, J.R. et al (1999) “Climate and atmospheric history of the past 420,000 years from the Vostok ice core, Antarctica “ Nature , 399, 429-436 The cyclical variations are linked to changes in the Earths orbit around the sun
Climate over the last 1000 years Ice cores provide a useful indication of long term climate changes but rather more detailed estimates of climate over the historical period have been developed. A good example is the work by Michael Mann and colleagues (1999) which was quoted in the Intergovernmental Panel on Climate Change (IPCC) report in 2001 and is shown on the next slide.
Based on Mann et al (1999) “Northern Hemisphere Temperatures During the Past Millennium: Inferences, Uncertainties, and Limitations” Geophysical Research Letters , 26, 759-762 Source: http://www.newscientist.com/data/images/ns/cms/mg18925431.400/mg18925431.400-2_752.jpg
The Hockey Stick controversy The previous slide became known as the “hockey stick” and was widely criticised, principally by people who were not climate scientists. One of the main criticisms was that the “Little Ice Age” and “Medieval Warm Period” were not apparent but there is evidence that the cooling and warming in those periods occurred regionally rather that globally. The next slide shows a number of other temperature series over the same time period and they all generally replicate the pattern produced by Michael Mann.
Climate during the instrumental period While the previous slides have mainly shown estimates of global temperatures from ice cores and proxy data (such as tree rings), actual observations of temperature are available across the world from the mid 19 th Century. These are more reliable than proxy data. Some people have tried to claim that such series have been influenced by the “urban heat island” effect but that effect is local and does not apply to ocean temperatures or those from remote areas and the series have been checked to ensure there is no significant heat island effect.
Some people have suggested the warming stopped in 1998 http://www.ipcc.ch/graphics/ar4-wg1/jpg/fig-3-1.jpg The change in average global temperature from 1850-1899 to 2001-2005 is about 0.8 o C. That may not seem much but it is actually a very large change in global terms.
Solar Activity The sun provides virtually all of the energy of the Earth (there is a very small amount of geothermal heat) as was shown on the energy balance slide. However, solar output does vary by small amounts. Some people have argued that changes in solar activity are the cause of climate changes over the last few hundred years. The sunspot “Maunder Minimum” occurred at one of the coldest parts of the “Little Ice Age”. But do the records of sunspots and solar output show a significant link with recent climate changes?
Global temperatures (red lines) and total solar irradiance (blue lines). The strong global warming in the last 30-35 years does not appear to be linked to solar output. Slide kindly donated by Alex Hill, Met Office
http://data.giss.nasa.gov/gistemp/2008/Fig4.gif Observed variation in solar output over the last 34 years
Source: http://www.cru.uea.ac.uk/cru/info/warming/ The period 2001-2009 (0.43°C above 1961-90 mean) is 0.19°C warmer than 1991-2000 (itself 0.24°C above 1961-90 mean). This is despite solar output falling through the 2000s and cooling in 2008 due to La Nina. Although air temperature rises appear to have levelled off in the 2000s, Trenberth (2010) has noted that in the oceans “substantial warming may be taking place below the upper 700 m” K.E. Trenberth Nature , 465, 20 May 2010 Global temperatures to 2009
It is not just temperatures that are changing Sea levels are rising around the world and many places are at risk from flooding especially islands like the Maldives and low lying countries such as Bangladesh. In Scotland some of that sea level rise is counteracted as the land is still rising after the last ice age (the deep ice pushed the land surface down). There are also precipitation changes across the world increases cause flooding and decreases can cause droughts. Sea level rise is shown on the next slide
Sea Level Rise ~20cms Slide thanks to Alex Hill.
What has happened in the UK and Scotland? Gordon Manley developed the Central England Temperature (CET) series which is the longest reliable temperature series in the world. It has been maintained and updated by the Met Office and provides a very useful record of temperatures in the recent past. The following slides show the average annual CET values and the standard 30 year averages starting with 1661-1690. The Met Office uses averages over 30 year periods. The current average is 1971-2000 and at the end of this year there will be a new 1981-2010 average.
Note the large inter-annual variability
1661-1690 updated every 10 years through to 1981-2010
http://ukclimateprojections.defra.gov.uk/images/stories/Trends_images/T_300dpi/T_Fig2.12b.png Average UK Summer Maximum Temperatures ( o C) Maximum temperatures in the North of Scotland have warmed by 1.3 o C from 1961 to 2006
http://ukclimateprojections.defra.gov.uk/images/stories/Trends_images/T_300dpi/T_Fig2.42.png Average UK Annual Precipitation (mm). Annual precipitation in the North of Scotland has increased by 23% from 1961 to 2006 and winter precipitation has increased by nearly 66%. Summer precipitation in the North of Scotland has fallen by 5% over the same period.
What has been the impact of the recent changes in this part of the world? One local example is the change in the number of days of skiing in the Cairngorms which is shown on the next two slides.
Human activity and climate change While there are long term changes in climate, we are increasing the concentration of the greenhouse gases and that increase will cause climate change over the next 100 hundred years and beyond.
How have greenhouse gas concentrations changed? Carbon dioxide Methane
Nitrous oxide As well as naturally occurring greenhouse gases we invented Halocarbons which are strong greenhouse gases and the amount of those gases is increasing. Low-level (tropospheric) ozone has also become important and it is formed due to sunlight acting on unburned motor vehicle fuel in exhaust fumes.
Modelling Climate Change AOGCMs Atmosphere Ocean General Circulation Models The models are complicated, for example HadCM3 has 19 atmospheric levels and 20 ocean levels. As well as modelling the impact of increased greenhouse gas concentrations on atmospheric and oceanic circulations, sea ice dynamics are modelled as are links to plants and soils. Further model input comes from the IPCC scenarios of human behaviour which allow for greater or less economic growth and for changes in behaviour (such as using more or less fossil fuels). Many governments are committed to cutting greenhouse gas emissions but high economic growth rates in India and China will have an important impact.
Source: IPCC (2007) Climate Change 2007 Working Group I Predicted changes in global temperature
What do the models predict? Temperature change ( o C) Sea level rise (m) Scenario Best Estimate Range Range B1 1.8 1.1 – 2.9 0.18 – 0.38 A1T 2.4 1.4 – 3.8 0.20 – 0.45 B2 2.4 1.4 – 3.8 0.20 – 0.43 A1B 2.8 1.7 – 4.4 0.21 – 0.48 A2 3.4 2.0 – 5.4 0.23 – 0.51 A1F1 4.0 2.4 – 6.4 0.26 – 0.54 The IPCC (2007) stated that it has a “ very high confidence that the global average net effect of human activities since 1750 has been one of warming” (that is, there is a 9 out of 10 chance that the warming is due to human activity) , and that: “ Continued greenhouse gas emissions at or above current rates would cause further warming and induce many changes in the global climate system during the 21st century that would very likely be larger than those observed during the 20th century. Source: IPCC (2007) Climate Change 2007 Working Group I
How reliable are these models? No model is perfect but models are being improved all the time. The Met. Office Hadley Centre climate modelling is regarded as some of the best in the world. We can only test the predictions against past climate and the models appear to simulate past climate well. One analogy is weather forecasting – it may often seem to be wrong where you are but actually the large pattern is modelled very well. So what do the predictions mean for Scotland? The following slides are from the UK Climate Projections UKCP09 and show the sort of climate changes we can expect.
Coire an t-Sneachda, Cairngorm, mid-June Typical mountain scene in June during the 1960s to 1980s
Change in annual mean temperature ( o C) High emissions scenario 2020’s 2050’s 2080’s Source: UKCP09 http://ukclimateprojections.defra.gov.uk/content/view/1457/499/
Coire an t-Sneachda, Cairngorm, mid-June The future scene in the mountains in June?
There is clear evidence human activity is causing climate change.
Temperatures will rise, melting ice and causing more heat waves. Rainfall patterns will change, causing floods and droughts. Sea levels will rise causing coastal flooding and there will be habitat loss and major impacts on wildlife and plants on land and at sea.
Changes are at the higher end of the predictions (4 to 6 deg C) will have severe impacts in all countries (the change from the last Ice Age was about 5 deg C!).
If we are wrong and climate doesn’t get warmer (very unlikely), we might simply be using renewable fuels sooner rather than later, as fossil fuels will run out!