2002 Recent Climate History - The Instrumental Era. Figure 1. Reconstructed surface temperature record. Strong warming in the first and late part of the century. El Ninos and major volcanic eruptions are noted. From Ruddiman. back http://data.giss.nasa.gov/gistemp/graphs/ 1
Figure 1. Illustrates an estimate of the average surface temperature of Earth over the last century. See http://www.giss.nasa.gov/research/observe/surftemp/ for much more detail. In Figure 2, a few of the longer records are shown. For an individual record, the warming does not generally exceed the climate noise, and in fact cooling predominates at some locations (e.g. Russia). Construction of temperature history, even during the instrumental period is quite difficult. In the early part of the century, the record is very sparse. (Figure from Hanson et al., JGR, 104, 30997, 1999). Coverage in the southern hemisphere and in the tropics is poor. Some records are contaminated by urban heat island effects. (Figure from Hanson et al., JGR, 104, 30997, 1999). Other sites have had changes in location of the measurement; others suffer from large shifts associated with changes in instrumentation. As the surface coverage has improved, the ability to define temperature anomalies has improved. Figure from Hanson Figure 2. Within the warming trend, large geographical variation is observed. Ruddiman. back 2
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back Global annual surface temperature relative to 1951-1980 mean based on surface air measurements at meteorological stations and satellite measurements of sea surface temperature http://data.giss.nasa.gov/gistemp/graphs/ 4
First discriminants of interdecadal variations in (a), (b) January and (c), (d) July temperatures. The discriminating patterns (a) and (c) and canonical variates (b) and (d) represent temperature changes relative to the 1916 98 mean, local changes being products of the canonical variate and the local values of the associated discriminating pattern. The discriminants are normalized such that the canonical variates have unit variance. In the amplitude time series (b) and (d), black lines indicate unfiltered canonical variates and red lines indicate low-pass filtered canonical variates. http://www.gps.caltech.edu/~tapio/discriminants/animations.html Schneider, T. J. Climate 14, 249 254, 2001. Discriminants of Twentieth-Century Changes in Earth Surface Temperatures 5
Sulfate Aerosol Sulfur plays an important part in forcing Earth s climate. Although not as important as for Venus, sulfate aerosol formation can significantly increase the albedo. Sulfur is emitted to the atmosphere as either reduced sulfur, such as H 2 S and DMS ((CH 3 ) 2 S) both of which are produced in biological processes in the surface ocean. In addition, SO 2 is emitted by both anthropogenic activity (combustion of sulfur containing fossil fuels), and in volcanoes. The sulfur is oxidized to S(IV), H 2 SO 4, by either: or: OH + SO 2 HOSO 2 HOSO 2 + O 2 HO 2 + SO 3 SO 3 + 2 H 2 O H 2 SO 4 + H 2 O SO 2 + H 2 O 2 H 2 SO 4 (in aerosol). H 2 SO 4 has extremely low vapor pressure. It either nucleates to form new particles or condenses on existing particles. The resulting particles do not absorb visible light significantly, but do scatter this radiation, increasing the planetary albedo. The effects of sulfate are obvious in the climate record following large volcanic eruptions that increase the scattering in the stratosphere (See Figures). Following concerns about acidification of lakes in the eastern US, the EPA regulated sulfur emissions. With concern about visibility in the west (e.g. LA, Grand Canyon), sulfur emissions greatly reduced. Estimates only a few years ago suggested Chinese emissions of sulfur would grow exponentially. In the last 5 years, it has been suggested that sulfur emission from China have actually fallen. Stratospheric sulfate and cooling following the eruption of Mt. Pinatubo. 6
From Ruddiman. J. Climate, 10, 245, 1997 7
Space based observations of SO 2 25.5 million tons of SO 2 was emitted by Chinese factories in 2005 up 27% from 2000 8
The last 1000 years The past 1000 yrs are particularly important time-frame for climate studies. If an accurate record of temperature can be constructed, climate variability (or noise ) can be evaluated and changes measured during the modern instrumental period can be compared. In the last 1000 years, orbital forcing has not changed significantly (though sun-climate interactions on shorter time scales remain an active area of research). In addition, estimates of volcanic and solar climate forcings are also robust over this time horizon. Proxy for Temperature Boreholes. In the figure below, the temperature recorded in numerous boreholes is corrected for thermal diffusion from deep in the Earth. A thermal wave appears to be propagating from the surface suggesting a ~. 7 degree recent warming. Thermal modeling suggests that the warming is relatively recent (last 200 years). Boreholes (as well as ocean sedimentary records) are relatively slow. Temperature-depth profiles measured in boreholes. 439 reduced temperature profiles are shown for northern midlatitudes. Ground warming of 0.7 degrees C is measured. The depth of penetration constrains the warming to the last 200 years. Harris and Chapman, GRL, 28, 747 (2001). 9
Tree rings. Tree ring records of past climate are precisely dated and annually resolved and can be calibrated using the last 100 yrs of instrumental record. Typically the width and density of the annual growth rings is used to estimate temperature. Large scale climate variability (e.g. ENSO; Arctic oscillation) are recorded in the tree rings. There are several biases that need to be mentioned. Trees grow on land (so no ocean record). Tree ring density or width actually reflect a complex biological response to climate (and other forcing) and the response can change over time. CO 2 fertilization may influence tree growth rate, particularly for high elevation drought-sensitive trees. Thus, tree ring data can not be used in isolation to develop a climate record. Corals. As with trees, surface corals record climate variation as variations in skeletal density and geochemical characteristics such as variation in trace elements or stable isotopes. Ice Cores. Ice cores from polar (and now tropical) regions can provide several climate related indicators. These include 18 O/ 16 O, ice accumulation rate, concentration of various salts and acids, time implied atmospheric loading of pollen, and trace gases such as CH 4 and CO 2. Lake and Ocean Sediments. Annually laminated lake sediments offer important archives of palaeo conditions. IPCC, AR4 WG1 2007 Records of NH temperature variation during the last 1.3 kyr. (a) Annual mean instrumental temperature records, identified in Table 6.1. (b) Reconstructions using multiple climate proxy records, identified in Table 6.1, including three records (JBB..1998, MBH..1999 and BOS..2001) shown in the TAR, and the HadCRUT2v instrumental temperature record in black. (c) Overlap of the published multi-decadal time scale uncertainty ranges of all temperature reconstructions identified in Table 6.1 (except for RMO..2005 and PS2004), with temperatures within ±1 standard error (SE) of a reconstruction scoring 10%, and regions within the 5 to 95% range scoring 5% (the maximum 100% is obtained only for temperatures that fall within ±1 SE of all 10 reconstructions). The HadCRUT2v instrumental temperature record is shown in black. All series have been smoothed with a Gaussian-weighted filter to remove fluctuations on time scales less than 30 years; smoothed values are obtained up to both ends of each record by extending the records with the mean of the adjacent existing values. All temperatures represent anomalies ( C) from the 1961 to 1990 mean. 10