Tim Osborn. Yann Arthus-Bertrand / Altitude

Transcription

1 Observations: Atmosphere and Surface Information from Paleoclimate Archives Tim Osborn A Lead Author of Chapter 5 (Information from Paleoclimate Archives) Climatic Research Unit, School of Environmental Sciences, University of East Anglia Yann Arthus-Bertrand / Altitude

2 Warming of the climate system is unequivocal Atmosphere and oceans have warmed, amounts of snow and ice have diminished, sea level has risen and GHG concentrations have increased

3 Each of the last three decades has been successively warmer y at the Earth s surface than any preceding decade since 1850 SPM.1b) C 2013, Fig. S (IPCC

4 Each of the last three decades has been successively warmer y at the Earth s surface than any preceding decade since 1850 SPM.1a) C 2013, Fig. S (IPCC

5 SPM.1a) C 2013, Fig. S (IPCC The rate of surface warming over the past 15 years ( [ to+015] C/decade) +0.15] is smaller than the warming rate since 1951 (0.12 [0.08 to 0.14] C/decade) The possible causes of this slowdown, and its implications for climate models and for our understanding of the climate system, are explored in the report

6 Over , almost the entire globe has experienced warming (from the NCDC MLOST dataset) M.1c) (IPCC 2013, Fig. SPM

7 Results similar for different datasets, though spatial coverage depends on the degree of interpolation (from the NCDC MLOST dataset) Research challenge: Improving temperature datasets, spatial and temporal coverage, biases & transparency (IPCC 2013, Fig )

8 trends from HadCRUT4

9 trends from Cowtan and Way (2013) trends from Cowtan and Way (2013) Infilling (kriging) missing regions within HadCRUT4

10 Cowtan & Way HadCRUT4 (plus uncertainties) E ti ti t t i i i ithi H dcrut4 Estimating temperatures over missing regions within HadCRUT4 increases the warming trend over the last 16 years

11 Trends in zonal mean temperatures highlight the uncertainty in the infilling reliant on sparse data and on differences between lower troposphere and surface temperatures HadCRUT4 Cowtan & Way

12 The climate system has continued to warm, even when surface warming has slowed Ocean heat uptake not necessarily an explanation for slowdown in surface warming, but it does demonstrate continuing imbalance in climate system energy budget 3, Fig. 1 of Box 3.1) (IPCC 201 ZJ = zetta Joules = J

13 In the Northern Hemisphere, was likely the warmest 30-year period of the last 1400 years (medium confidence) What is the basis for this statement?

14 g. 5.7) PCC 2013, Fig (IP 14 reconstructions from 12 studies Some tree-ring, others use multiple proxies with/without tree-rings Timing of relatively warm/cold periods is similar but size of changes can be quite different High confidence that start and end of the last millennium were warmer than the average for the whole millennium Relative warmth of medieval and modern periods much more uncertain

15 Using published uncertainty ranges, each reconstructed 30-year mean is very likely cooler than the most recent 30-years of instrumental temperature Published uncertainty ranges do not represent all sources of error, especially long-term representation of temperature by some proxies Despite 8 reconstructions suggesting very likely, assessment was only likely that recent temperatures were warmest of the last 1400 years Confidence in this assessment is only medium because only medium amount of independent evidence & evidence only has medium reliability Fewer proxy records back to 1000 CE or earlier, so reconstructions are less independent of each other & results more susceptible to errors in individual proxy records Other supporting evidence that the modern period is warmer Medieval period: only small variations in sea level & [CO2], glacier response was more heterogeneous & complex than the near-global glacier recession observed at present, reconstruction of past radiative forcings, detection ti of the influence of these forcings on the reconstructions ti

16 (IPCC 2013, Fig. 5.8) Model-data comparisons

17 Research challenge: Research challenge: Defining pre-industrial climate as the baseline for policy targets (e.g. no more than 2 C above pre-industrial) g. 5.8) PCC 2013, Fig (IP

18 Paleoclimate li and sea levell during the last interglacial and under high CO 2 conditions

19 Ice core records of fghgs now extended to 800, years Highest resolution records also allow rates of change to be estimated High confidence that current rates of GHG increase exceed those of the last 22,000 years 13, Fig. 5.3) (IPCC 20

20 Climate & ice sheet models can simulate many aspects of the glacialinterglacial cycles Models (shading) driven by variations in orbital parameters & GHG concentrations (IPCC 20 13, Fig. 5.3)

21 Last interglacial (Eemian) characterized by higher temperatures and higher sea level than Holocene Sea level 5 to 10 m higher than present day, best estimate ~ 6 m (IPCC 2013, Fig. 5.3)

22 Last interglacial (Eemian) characterized by higher temperatures and higher sea level than Holocene Sea level 5 to 10 m higher than present day, best estimate ~ 6 m (IPCC 2013, Fig. 5.16) New NEEM ice core: Greenland did not melt completely Selecting from ensemble of model simulations, those consistent with ice core data give 1.4 to 4.3 m contribution to sea level from Greenland ice sheet Implying a significant contribution from the Antarctic ice sheet (medium confidence) (note different orbital forcing and high-latitude temperature, averaged over several thousand years, at least 2 C warmer than present)

23 g. 5.2) PCC 2013, Fig (IP Geological CO 2 proxies: significant uncertainties remain, though progress in process understanding & reconciliation Mid-Pliocene Warm Period & subsequent 300 kyr: CO ppm Global temperature estimates in range 1.9 to 36 C 3.6 above pre-industrial Sea level higher than present (amount uncertain, up to 20 m) due to mass loss from Greenland, West Antarctic and possible East Antarctic ice sheets

24 (IPCCC 2013, Fig. SPM.1a)

25 Early Eocene (52 to 48 million years ago) CO 2 exceeded 1000 Early Eocene (52 to 48 million years ago) CO 2 exceeded 1000 ppm (medium confidence) Global temperatures 9 to 14 C above pre-industrial (medium confidence) Ocean and continental configurations different from today SPM.1a) C 2013, Fig. S (IPCC

26 Changes in the hydrological cycle

27 CC 2013, Fig. SPM.2) (IPC Confidence in global-mean land precipitation p change is medium since 1951 but low low prior to 1951 Over NH mid-latitudes, land precipitation has increased since 1901 (medium confidence) and since 1951 (high confidence) For other latitudes, area-averaged long-term positive or negative trends have low confidence

28 CC 2013, Fig. SPM.2) (IPC Research challenge: Improving global precipitation datasets (though note low confidence partly arises because area averaged changes (though note low confidence partly arises because area averaged changes are small compared to high spatial variability and because long-term trends are small compared to temporal variability)

29 Overall increase (H, but Sv) Overall increase (H) More increases than decreases (H, but SV)? (L)? (L)? (L) More increases More increases? (L) than decreases than decreases (M, but SV) (M, but SV) Overall decrease (H, but Sv) Confidence: H=high, M=medium, L=Low SV=spatial variability Heavy precipitation: likely more land areas with increases than decreases (derived from IPCC 2013, Table 2.13)

30 Warming of the climate system is unequivocal Atmosphere and oceans have warmed, amounts of snow and ice have diminished, sea level has risen and GHG concentrations have increased

31 Spare slides

32 SPM.1a) C 2013, Fig. S (IPCC Warming of the climate system is unequivocal Atmosphere and oceans have warmed, amounts of snow and ice have diminished, sea level has risen and GHG concentrations have increased

33 Atmospheric CO 2 Ocean pco 2 Ocean ph Atmospheric methane (IPC CC 2013, Fig g. TS.5) Atmospheric O 2 Recent changes in CO 2 and CH 4 O 2, carbon isotopes etc. demonstrate anthropogenic origin of CO 2 increase Measured decrease in ocean alkalinity li it (decreased d ph) CH 4 began increasing again in 2007 after stable decade, drivers not clear

34 Last Interglacial (Eemian) g ( ) Annual data and simulations of geographic patterns, and seasonal zonal means SPM.1a) C 2013, Fig. S (IPCC