1 3.4 Observations Most figures are from latest IPCC report (2013) unless otherwise stated – see: #.Un_txCQp2qA

2 3.4 Observations Need to consider: Instrumental climate record of the last century or so Recent changes in greenhouse gases and other quantities

3 Important Questions Concerning the Climate Record How much is the world warming? Is the recent warming unusual? How rapidly is climate changing compared to earlier changes? Have precipitation and atmospheric moisture changed? Are atmospheric/oceanic circulations changing? Has climate variability (e.g., extremes) changed?

4 Observed Climate Variables Temperature (global mean, regional, diurnal range, upper air...) Precipitation, humidity, cloud cover Snow cover Sea-ice thickness and extent Natural modes (El Nino, North Atlantic Oscillation, Atlantic Multidecadal Oscillation) Climate extremes

5 Use of ‘Anomalies’ Anomalies are changes relative to some particular reference period used to emphasise positive and negative excursions around a long-term mean

Plants releasing CO2 Plants absorbing CO2 The Keeling Curve (named after Dr. Charles Keeling, Scripps)

316 ± 2 ppm 398 ± 3 ppm

300 Previous CO 2 maximum ~300 ppm Previous CH 4 maximum ~780 ppb Neither CO 2 nor CH 4 have been this high in the past 800,000 years Has CO 2 been this high over the past 800,000 years?

Detection of our increasing carbon emissions – one of the most important scientific breakthroughs of the past 150 years

10 Surface Temperature Changes Given our knowledge of the greenhouse effect we would expect that any increase in greenhouse gases would cause a warming of the earth’s surface.

Recent Warming (IPCC 5 th Assessment, 2013) Observed global mean combined land and ocean surface temperature anomalies, from 1850 to 2012 from three data sets Top panel: annual mean values Bottom panel: decadal mean values including the estimate of uncertainty for one dataset (black). Anomalies are relative to the mean of 1961−1990. Each of the last three decades has been successively warmer at the Earth’s surface than any preceding decade since 1850

Trends 12

Land-Surface Air Temperature (LSAT) LSAT temperatures have increased from.08 to.27°C/decade since 1880, depending on how you determine the fit This reanalysis includes four different data sets, using different techniques Careful study to address concerns about station sites, data distribution, have been taken into account In summary, it is certain that globally averaged LSAT has risen since the late 19 th century, and that this warming has been particularly marked since the 1970s. Global annual average land-surface air temperature (LSAT) anomalies relative to climatology from four different datasets

Changes in Climate “Normals” from to Averages NOAA Data\ Changes in Climate “Normals” from to Averages NOAA Data\ Climate “Normals” are 30-year averages of NOAA climatological data (

Sea Surface Temperatures (SSTs) Measurements of sea surface temperature are available from buckets, engine room intake, hull contact sensors, moored and drifting buoys, and satellites Careful data analysis needed (measurement biases and validation) Nonetheless, certain that global average sea surface temperatures (SSTs) have increased since the 1950s, as well as since the beginning of the 20 th century Global average SST relative to climatology from gridded (interpolated) data sets. Interpolated (solid), non-interpolated (dashed).

Global Temperature (Land and Sea) All 10 of the warmest years in the record have occurred since and 2005 tied for warmest in all three data sets Global mean trends are significant for all data sets HadCRUT4 – warming from (early- industrial) to average is 0.61°C ±0.06°C (90% confidence) Decadal global mean surface temperature (GMST) anomalies

17 Spatial Pattern of Surface Temperature Changes Trends in Global Mean Surface Temperature (GMST) from the three datasets of Figure 2.20 for 1901–2012. White areas indicate incomplete or missing data. Trends have been calculated only for those grid boxes with greater than 70% complete records and more than 20% data availability in first and last decile of the period. Black plus signs (+) indicate grid boxes where trends are significant (i.e., a trend of zero lies outside the 90% confidence interval).

18 Spatial Pattern of Surface Temperature Changes Trends in Global Mean Surface Temperature (GMST) from NCDC MLOST for three non-consectutive shorter periods (1911–1940; 1951– 1980; 1981–2012). White areas indicate incomplete or missing data.

19 Summary of Surface Temperature Changes It is certain that globally averaged near surface temperatures have increased since the late 19 th century. Each of the past three decades has been warmer than all the previous decades in the instrumental record, and the decade of the 2000s has been the warmest. The global combined land and ocean temperature data show an increase of about 0.89°C (0.69°C–1.08°C) over the period 1901–2012 and about 0.72°C (0.49°C–0.89°C) over the period 1951–2012 when described by a linear trend. Despite the robust multidecadal timescale warming, there exists substantial multi-annual variability in the rate of warming with several periods exhibiting almost no linear trend (including the warming hiatus since 1998).

20 Upper Air Temperatures Weather balloons (radiosondes) –T at discrete levels –Difficulties with changes in instruments Satellite (Microwave Sounding Unit – MSU and stratospheric Sounding Unit - SSU) since 1979 –T over broad regions –Problems with orbit drift, calibration, etc. -> spurious T trends

21 Upper Air Temperatures

Upper Air Temperatures - Summary In summary, based upon multiple independent analyses of measurements from radiosondes and satellite sensors it is virtually certain that globally the troposphere has warmed and the stratosphere has cooled since the mid-20th century. Despite unanimous agreement on the sign of the trends, substantial disagreement exists among available estimates as to the rate of temperature changes, particularly outside the Northern Hemisphere extra-tropical troposphere, which has been well sampled by radiosondes. Hence there is only medium confidence in the rate of change and its vertical structure in the Northern Hemisphere extra-tropical troposphere and low confidence elsewhere. 22

Changes in the Hydrological Cycle: Precipitation 23

Changes in the Hydrological Cycle: Precipitation 24

Changes in the Hydrological Cycle: Precipitation 25 In summary, the land areas of the mid-latitudes of the NH show a likely overall increase in precipitation (medium confidence since 1901, but high confidence after 1951). Since 1951, precipitation in the high latitudes of the NH also shows increases, but confidence is low for the changes in this region. There is evidence for increased precipitation in the mid-latitudes of the SH since 1901 (medium confidence). It is likely there was an abrupt decline in SH mid-latitude precipitation in the early 2000s consistent with enhanced drying that has very recently recovered. Precipitation in the tropical land areas has increased (medium confidence) over the last decade, reversing the drying trend that occurred from the mid-1970s to mid-1990s reported in AR4. Consequently, there is little evidence for longer term changes in tropical precipitation over land.

Changes in the Hydrological Cycle: Specific Humidity 26

Changes in the Hydrological Cycle: Total Column Water Vapor 27

Changes in the Hydrological Cycle: Total Column Water Vapor 28 In summary, radiosonde, GPS and satellite observations of tropospheric water vapour indicate very likely increases at near global scales since the 1970s occurring at a rate that is generally consistent with the Clausius-Clapeyron relation (about 7% °C –1 ) and the observed increase in atmospheric temperature. Significant trends in tropospheric relative humidity at large spatial scales have not been observed, with the exception of near-surface air over land where relative humidity has decreased in recent years.

29 Changes in the Cryosphere Snow cover Sea-ice extent Mountain glaciers - Average Arctic temperatures have increased at almost twice the global average rate in past 100 years. WMO International Polar Year

30 Observed Northern Hemisphere Snow Cover TOP Annual snow-cover extent decreased by 10% since 1966 Mostly accounted for by spring/summer since 1980s BOTTOM Annual snow cover anomalies correlate with T (dashed line)

Observed Northern Hemisphere Sea-Ice Extent -sea-ice-minimum-in-2013-is-sixth-lowest- on-record/#.UoA_0iQp2qB

32 Observed Northern Hemisphere Sea-Ice Extent Summer minimum Arctic sea ice extent If trend continues Arctic will be ice-free by ~2050

NASA Goddard Space Flight Center (orange line shows average minimum ice extent (for period) has lowest sea ice extent in more than 30 years. Observed Northern Hemisphere Sea-Ice Extent

Observations of glacier retreat Jahn [1931]; Schubert [1992, 1999] < 2 km 2 of ice left in Venezuela Glacier Espejo, Pico Bolivar (5002 m) Venezuela

35 Observed Mountain Glacier Length 169 glacier length records Glacier retreat is worldwide

Update from latest IPCC report (2013) 36

37 Summary of Observed Cryospheric Changes Consistency of cryospheric changes and temperature changes NH snow cover correlates well with spring temperature changes Reduced sea-ice extent consistent with increases in spring temperatures Small changes in Arctic winter ice, despite large changes in winter T Major retreat of glaciers consistent with 20 th - century T changes

IPCC, AR4, WG1, 2007; BAMS, Aug How much has sea level gone up in the 20th century? Red: reconstructed (+ 90% confidence intervals) Blue: coastal tide gauge measurements Black: satellite altimetry Current global sea level rise: 3.5 mm/yr

Sea-level Rise 39

IPCC, AR4, WG2, 2007 What places will be most affected by sea-level rise by 2050 ? Extreme:> 1 million people displaced High: > 50,000 people displaced Medium > 5,000 people displaced

41 Atmospheric/Oceanic Circulations (El Nino) Occurrence of strong El Ninos may be higher since 1980s But significance is low due to strong contribtion of natural variability

42 Atmospheric/Oceanic Circulations (NAO) North Atlantic Oscillation (NAO) is a measure of circulation patterns in the NH Positive index implies warmer Europe Greater occurrence of positive indices since 1980s NAO trending towards negative values recently. Difficult to separate natural variability and long-term change

43 Climate Extremes (extreme temperatures) Trends in days/decade (relative to ). 10 th percentile 90 th percentile

44 Climate Extremes (heatwaves)

45 Climate Extremes (precipitation) Contribution from ‘very wet’ days (95 th precentile) to total decadal precipitation.

Precipitation Increases in amounts of very heavy precipitation ( ) 46 The map shows percent increases in the amount falling in very heavy precipitation events (defined as the heaviest 1 percent of all daily events) from 1958 to 2007 for each region. There are clear trends toward more very heavy precipitation for the nation as a whole, and particularly in the Northeast and Midwest (updated from Groissman et al,2004)

Next Section Next lecture will be concerned with modeling results Key for interpreting the causes of climate change Key for making projections 47