Climate Change Challenge

Measuring Past Climate Change

There are many ways by which scientists attempt to unlock the historical climate record archives of the past – from looking at sediments from many meters below the present day seabed, to tree rings, stalagmite analysis to analysis of fossil shells less than 1mm in size. The following gives a few examples of how science is trying to interpret the natural climate cycles from the past.

By drilling ice cores miles into the frozen ice in Greenland and in the Antarctic we can get a detailed temperature and CO2 history of Earth's past. By obtaining an ice core sample 10,000 feet down in our ice sheets we are looking at ice made over 700,000 years ago and by analysing the minute bubbles of air trapped in this ice scientists can tell what the earth's temperature was at the time.

In Figure 1Graph of CO2 (green), reconstructed temperature (blue) and dust (red) from the Vostok ice core for the past 420,000 years. alongside, the graph gives the temperature, carbon level and dust history of the planet over the past 420,000 years. Warm peaks interrupt long periods of cold ice age conditions and it is easy to see the direct correlation between temperature and CO2 levels: as the greenhouse gases in the atmosphere rise, so does the temperature. During the last 14,000 years the earth has had one of its most stable periods in terms of temperature with small fluctuations of only 1 degree centigrade - this coincides directly with the stable period of 'civilisation' as we know it - conditions on Earth are ideal for crop development, animal life and human existence.
Source: Reproduced from the IPCC, 2001

Sea level change was and still is documented using a system of global tide gauges, which when collated provides an invaluable record of fluctuations on a local, regional and global scale. This system is also capable of picking up extreme events, such as the size of tsunamis associated with the Krakatoa volcanic eruption in 1883 and their impact on global sea level. Modern measurements are now supplemented with satellite altimetry (sea surface height measured from space), and increasing research is being done into the use of uranium series and radiocarbon dating techniques on fossil corals.

Physical, chemical and biological changes in the oceans, indicative of changing climate, ocean / atmosphere interaction and ocean circulation patterns are researched in a number of ways. ARGO floats, that follow the ocean currents monitor temperature and salinity changes; geochemical signals contained in the shells of fossils, such as foraminifera, give indications as to the chemical make-up of the oceans when the shells were formed; distribution of certain species of forams, both modern and fossilised, that maybe favour shallow water or cold water help map changing oceanic conditions and circulation patterns; and the incidence of 18O (the heavy oxygen isotope) in sediments beneath the ocean floor gives some indication of extent of polar ice at the time the sediments were deposited – just a few of the many ways scientists investigate the role of the oceans and their reactions to a changing climate.

The World Glacier Monitoring Service collects annual information on glacier retreat and mass balance, managing an inventory of more than 100,000 glaciers covering an approximate area of 240,000km2.

Dendroclimatology is the analysis of tree rings to assess past climate – ring thickness can be indicative of growing conditions, with large thick rings suggesting a fertile growing period and thin rings suggesting climatic hardship for the tree.

Palynology is the study of pollens, and the distribution of species with known climatic preferences. Pollens found in sediments can be used to infer the geographical spread of a species, and so track changes in vegetation throughout Quaternary glacial and inter-glacial periods.

Historical and archaeological documents and oral stories can also give scientists insight into past abrupt climate change or extreme weather events in periods when accurate measuring systems were not in place. One example of this is the Little Ice Age. Snowy paintings of Pieter Brueghel the Elder and documentation of the first River Thames Frost Fair in 1607, both depict the Little Ice Age that affected Europe and North America. However, Mayan and Aztec chronicles from the Yucatan Peninsula talk about cold and drought at the same time, whilst sediment cores from Lake Malawi in southern Africa show colder conditions between 1570 and 1820, and a 3000 year temperature reconstruction of a stalagmite from a cave in South Africa shows a cold period from 1500-1800, suggesting that the Little Ice Age affected a large proportion of the globe.

Atmosphere

The fundamentals of climate change have long been understood because they involve the same basic physics that keeps the earth habitable. Heat-trapping 'greenhouse gases' in the atmosphere (of which the two most important are water vapour - clouds- and carbon dioxide, CO2) let through short wave radiation from the sun but absorb the long wave heat radiation coming back from the Earth's surface and re-radiate it (Figure 2)Atmospheric concentrations of CO2, CH4 and N2O over the last 10,000 years (large panels) and since 1750 (inset panels). Measurements are shown from ice cores (symbols with different colours for different studies) and atmospheric samples (red lines). The corresponding radiative forcings relative to 1750 are shown on the right hand axes of the large panels.. These gases act like a blanket - and keep the surface and the lower atmosphere about 33°C warmer than it would be without them. The Earth's greenhouse blanket is a good balance between the extremes of our neighbours: Mars, which has no greenhouse gases is a frozen wasteland; whilst Venus remains trapped in a dense blanket of CO2 and is consequently a very hot and hostile place.
Source: The Carbon Trust, UK

Global atmospheric concentrations of CO2, CH4 and N2O have increased markedly as a result of human activities since 1750 and now far exceed pre-industrial values determined from ice cores spanning many thousands of years (Figures 3Illustration of the greenhouse effect and 4(a) Global annual emissions of anthropogenic greenhouse gases (GHGs) from 1970 to 2004.[5] (b) Share of different anthropogenic GHGs in total emissions in 2004 in terms of CO2-eq. (c) Share of different sectors in total anthropogenic GHG emissions in 2004 in terms of CO2-eq. (Forestry includes deforestation.)). The atmospheric concentrations of CO2 and CH4 in 2005 exceed by far the natural range over the last 650,000 years. Global increases in CO2 concentrations are due primarily to fossil fuel use, with land-use change providing another significant but smaller contribution. It is very likely that the observed increase in CH4 concentration is predominantly due to agriculture and fossil fuel use. The increase in N2O concentration is primarily due to agriculture.

Warming of the climate system is unequivocal, as is now evident from observations of increases in global average air and ocean temperatures, widespread melting of snow and ice and rising global average sea level. Eleven of the last twelve years (1995-2006) rank among the twelve warmest years in the instrumental record of global surface temperature (since 1850) (Figure 5Observed changes in (a) global average surface temperature; (b) global average sea level from tide gauge (blue) and satellite (red) data; and (c) Northern Hemisphere snow cover for March-April. All differences are relative to corresponding averages for the period 1961-1990. Smoothed curves represent decadal averaged values while circles show yearly values. The shaded areas are the uncertainty intervals estimated from a comprehensive analysis of known uncertainties (a and b) and from the time series (c).). The 100-year linear trend (1906-2005) of 0.74 [0.56 to 0.92]°C is larger than the corresponding trend of 0.6 [0.4 to 0.8]°C (1901-2000) given in the Third Assessment Report in 2001. The linear warming trend over the 50 years from 1956 to 2005 (0.13 [0.10 to 0.16]°C per decade) is nearly twice that for the 100 years from 1906 to 2005. Average Arctic temperatures have increased at almost twice the global average rate in the past 100 years.

The observed patterns of warming, including greater warming over land than over the ocean, and their changes over time, are best reproduced only by models that include anthropogenic forcing. No coupled global climate model that has used natural forcing only has reproduced the continental mean warming trends in individual continents (except Antarctica) over the second half of the 20th century (Figure 6Comparison of observed continental- and global-scale changes in surface temperature with results simulated by climate models using either natural or both natural and anthropogenic forcings. Decadal averages of observations are shown for the period 1906-2005 (black line) plotted against the centre of the decade and relative to the corresponding average for the 1901-1950. Lines are dashed where spatial coverage is less than 50%. Blue shaded bands show the 5 to 95% range for 19 simulations from five climate models using only the natural forcings due to solar activity and volcanoes. Red shaded bands show the 5 to 95% range for 58 simulations from 14 climate models using both natural and anthropogenic forcings.).
Source: IPCC, 2007: Climate Change 2007: Synthesis Report. Contribution of Working Groups I, II and III to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change [Core Writing Team, Pachauri, R.K and Reisinger, A. (eds.)]. IPCC, Geneva, Switzerland, 104 pp.

Oceans

Sea level rise is one of the major long-term consequences of human-induced climate change. Future projections of sea level changes and their regional expression are of crucial importance for the sustainability of coastal settlements around the world. However, process understanding was limited and thus both size and uncertainties associated with some of these contributions remained still largely unknown (for the IPCC Assessment Report published in 2007). The future dynamical behaviour of the large polar ice sheets of Antarctica and Greenland in a changing climate was identified as the primary origin of the large uncertainty in the projections of sea level rise for the 21st century.
Source: IPCC, 2010: Workshop Report of the Intergovernmental Panel on Climate Change Workshop on Sea Level Rise and Ice Sheet Instabilities [Stocker, T.F., D. Qin, G.-K. Plattner, M. Tignor, S. Allen, and P.M. Midgley (eds.)]. IPCC Working Group I Technical Support Unit, University of Bern, Bern, Switzerland, pp. 227.

Observations since 1961 show that the average temperature of the global ocean has increased to depths of at least 3000m and that the ocean has been taking up over 80% of the heat being added to the climate system. Global average sea level rose at an average rate of 1.8 [1.3 to 2.3]mm per year over 1961 to 2003 and at an average rate of about 3.1 [2.4 to 3.8]mm per year from 1993 to 2003 (Figure 5Observed changes in (a) global average surface temperature; (b) global average sea level from tide gauge (blue) and satellite (red) data; and (c) Northern Hemisphere snow cover for March-April. All differences are relative to corresponding averages for the period 1961-1990. Smoothed curves represent decadal averaged values while circles show yearly values. The shaded areas are the uncertainty intervals estimated from a comprehensive analysis of known uncertainties (a and b) and from the time series (c).). Whether this faster rate for 1993 to 2003 reflects decadal variation or an increase in the longer-term trend is unclear. Since 1993 thermal expansion of the oceans has contributed about 57% of the sum of the estimated individual contributions to the sea level rise, with decreases in glaciers and ice caps contributing about 28% and losses from the polar ice sheets contributing the remainder.

There is high agreement and much evidence that with current climate change mitigation policies and related sustainable development practices, global greenhouse gas (GHG) emissions will continue to grow over the next few decades (Figure 7Global greenhouse gas GHG emissions (in GtCO2-eq per year) in the absence of additional climate policies: six illustrative Special Report on Emissions Scenarios (SRES) marker scenarios (coloured lines) and 80th percentile range of recent scenarios published since SRES (post-SRES) (gray shaded area). Dashed lines show the full range of post-SRES scenarios. The emissions include CO2, CH4, N2O and F-gases. The A1 storyline assumes a world of very rapid economic growth, a global population that peaks in mid-century and rapid introduction of new and more efficient technologies. A1 is divided into three groups that describe alternative directions of technological change: fossil intensive (A1FI), non-fossil energy resources (A1T) and a balance across all sources (A1B). B1 describes a convergent world, with the same global population as A1, but with more rapid changes in economic structures toward a service and information economy. B2 describes a world with intermediate population and economic growth, emphasising local solutions to economic, social, and environmental sustainability. A2 describes a very heterogeneous world with high population growth, slow economic development and slow technological change.). If radiative forcing were to be stabilised, keeping all the radiative forcing agents constant at B1 (scenario where global population peaks mid Century with rapid changes in economic structures) or A1B (scenario where global population peaks mid Century with a balance across fossil fuel and non fossil fuel sources) levels in 2100, model experiments show that a further increase in global average temperature of about 0.5°C would still be expected by 2200. In addition, thermal expansion alone would lead to 0.3 to 0.8m of sea level rise by 2300 (relative to 1980-1999). Thermal expansion would continue for many centuries, due to the time required to transport heat into the deep ocean.
Source: IPCC, 2007: Climate Change 2007: Synthesis Report. Contribution of Working Groups I, II and III to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change [Core Writing Team, Pachauri, R.K and Reisinger, A. (eds.)]. IPCC, Geneva, Switzerland, 104 pp.

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Dr Carol Cotterill 2008

Carol Cotterill"Amazingly we picked a really interesting area and got some incredible results... This has been a good day. Not only have Dave and I managed to get two interesting profiles under our belt, but we have begun to raise interest amongst the artists onboard as to how they could take our work and incorporate it into theirs..."
Read the full blog post by Carol Cotterill, Marine and Coastal Geoscientist, during the 2008 Art/Science Expedition ›

Graph of CO2 (green), reconstructed temperature (blue) and dust (red) from the Vostok ice core for the past 420,000 years.
Atmospheric concentrations of CO2, CH4 and N2O over the last 10,000 years (large panels) and since 1750 (inset panels). Measurements are shown from ice cores (symbols with different colours for different studies) and atmospheric samples (red lines). The corresponding radiative forcings relative to 1750 are shown on the right hand axes of the large panels.
Illustration of the greenhouse effect
(a) Global annual emissions of anthropogenic greenhouse gases (GHGs) from 1970 to 2004.[5] (b) Share of different anthropogenic GHGs in total emissions in 2004 in terms of CO2-eq. (c) Share of different sectors in total anthropogenic GHG emissions in 2004 in terms of CO2-eq. (Forestry includes deforestation.)
Observed changes in (a) global average surface temperature; (b) global average sea level from tide gauge (blue) and satellite (red) data; and (c) Northern Hemisphere snow cover for March-April. All differences are relative to corresponding averages for the period 1961-1990. Smoothed curves represent decadal averaged values while circles show yearly values. The shaded areas are the uncertainty intervals estimated from a comprehensive analysis of known uncertainties (a and b) and from the time series (c).
Comparison of observed continental- and global-scale changes in surface temperature with results simulated by climate models using either natural or both natural and anthropogenic forcings. Decadal averages of observations are shown for the period 1906-2005 (black line) plotted against the centre of the decade and relative to the corresponding average for the 1901-1950. Lines are dashed where spatial coverage is less than 50%. Blue shaded bands show the 5 to 95% range for 19 simulations from five climate models using only the natural forcings due to solar activity and volcanoes. Red shaded bands show the 5 to 95% range for 58 simulations from 14 climate models using both natural and anthropogenic forcings.
Global greenhouse gas GHG emissions (in GtCO2-eq per year) in the absence of additional climate policies: six illustrative Special Report on Emissions Scenarios (SRES) marker scenarios (coloured lines) and 80th percentile range of recent scenarios published since SRES (post-SRES) (gray shaded area). Dashed lines show the full range of post-SRES scenarios. The emissions include CO2, CH4, N2O and F-gases. The A1 storyline assumes a world of very rapid economic growth, a global population that peaks in mid-century and rapid introduction of new and more efficient technologies. A1 is divided into three groups that describe alternative directions of technological change: fossil intensive (A1FI), non-fossil energy resources (A1T) and a balance across all sources (A1B). B1 describes a convergent world, with the same global population as A1, but with more rapid changes in economic structures toward a service and information economy. B2 describes a world with intermediate population and economic growth, emphasising local solutions to economic, social, and environmental sustainability. A2 describes a very heterogeneous world with high population growth, slow economic development and slow technological change.
Artist Amy Balkin in conversation with Dr Simon Boxall during the 2007 Art/Science Expedition
Dr Simon Boxall launching Arty Bob the ARGO float, during the 2007 Art/Science Expedition
Dr Simon Boxall at the helm during the 2004 Art/Science Expedition
Illustration showing sea surface temperature. National Oceanography Centre, Southampton
Emily Venebles and Dr Simon Boxall taking measurements during the 2007 Art/Science Expedition
The Gulf Stream, a warm water current the size of 30 Amazon Rivers, flows north along the surface of the North Atlantic... as it reaches the Svalbard Archipelago it falls to the ocean floor, a sinking action that helps to drive the whole 'global heat conveyor'.
Dr Carol Cotterill and Dr Simon Boxall launch Arty Bob, the ARGO float, during the 2007 Art/Science Expedition
Photograph by Ana Cecilia Gonzales Vigil
Satellite image showing sea surface temperature (SST). National Oceanography Centre, Southampton.
Tree sampling at Manu Learning Centre during the 2009 Andes Expedition
Satellite image of the High Arctic environment. Image: NASA.
Illustration of the greenhouse effect

Illustration of the greenhouse effect