An Arctic Perspective on Climate Change

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1 An Arctic Perspective on Climate Change 23 Oct 2012 Gifford Miller (and many others) University of Colorado Boulder

2 The Earth is warming How do we know?

3 Temperature Anomaly ( C) It s a fact Global Land Ocean Temperature Index.6.4 Annual Mean 5 year Running Mean Year AD Source: NASA

4 23 Sept 2012

5 GRACE (gravity) satellite pair shows that the rate of mass lost from Greenland by melting and calving is accelerating in recent years

6 Extreme Ice Survey (2009)

7 Spatial pattern of the temperature anomalies for the first decade of the 21 st Century wrt

8 Arctic Amplification If global climate warms or cools, regardless of forcing mechanism, feedbacks and interactions unique to the Arctic (primarily sea ice and snow cover) will amplify temperature change across the Arctic relative to the Northern Hemisphere average. modified from Serreze and Francis, Climatic Change, 2006 If global temperatures change, Arctic temperatures will change even more. Miller et al., 2010

9 Because of Arctic Amplification, the Arctic is ideal to place observed warming in a geological context

10 Limitations of historical record: how do we know the observed trend is not part of a longer cycle? Source: NASA Year AD

11 Summer Temperatures (J,J,A) Arctic Global Atlantic Multidecadal Oscillation (AMO) ~90 year cycle

12 Unforced natural climate variability on decadal timescales; is recent warming in part linked to a low-frequency natural cycle.

13 Natural Modes of Variability Do unforced multi-decadal cycles of temperature change explain some or all of the observed recent warming? The instrumental temperature record is too short to resolve this question. Forced Variability Planet adjusts its temperature in response to specific changes in terms that determine the planetary energy balance. Is recent warming a response to a known forcing?

14 To address whether current warming is outside the range of lowfrequency unforced climate variability requires that we look farther back than the instrumental record..paleoclimatology

16 At high northern latitudes ice caps The ice are caps the most are melting reliable monitors of past summer temperature changes. 90% of the annual glacier mass balance is explained by summer temperature (Koerner, 2005).

17 Cold ice caps on flat terrain do not erode; they preserve ancient landscapes (Falconer, 1966)

19 and they preserved the plants that they kill

20 M10-B236v

21 M10-B236v

22 M10-B236v

23 1235 ± 20 years ago Dates when snowline dropped below this site, and remained below (on average) until the current decade

24 Regrowth (mosses) or colonization occurs within 3 years, rapidly resetting the radiocarbon clock; dead plants are eroded by meltwater or wind.

25 C dates on dead veg from ~110 ice caps

26 Snowline ( aerial photography) with all dated sites and their collection elevation

27 We normalize by calculating the elevation difference between each collection site and its ~mid-20 th C snowline, and plot vs sample age.

28 Calibrated Years Ago Our data end ~400 yr ago

29 500 m snowline drop in 5000 years Based on surface lapse rate (5 C km -1 ), this represents 2.5 C decrease in mean summer temperature Why would summers cool during this interval? Calibrated Years Ago

30 Planetary Energy Balance 1. Sun s temperature (solar irradiance) 2. Earth-Sun distance No Yes 3. Earth s reflectivity (planetary albedo ~0.3) Yes 4. Earth s greenhouse effect Yes

31 Precession of the Equinoxes Currently, Earth is farthest from the Sun in NH Summer. ago

32 Orbitally-forced climate change For the past 11,000 years NH summer has occurred at increasing distances from the Sun. So we predict steadily cooler NH summers. ago 11,000 years ago there was 9% more solar energy in NH summer.

33 From First Principles We expect NH summers to be hottest 10-6 ka ago Gradual NH summer cooling Superimposed unforced variability

34 Veg Kill Dates Tell Us. Current summer temperatures are at least as warm as any century in the past 5000 years But 5 sites would not fit on that plot Calibrated Years Ago

35 C dates on dead veg from ~110 ice caps

36 45,500 ± 1310 yr BP

37 Rooted tundra plants exposed by recent melt at five ice caps gave dates between 41,000 and 47,000 years

38 UCIAMS Lab ID Field ID Elev (m asl) Distance from ice edge (m) 14 C age (cal years before present) ± 1s M10-B231v , M10-B232v 1396 <0.5 41, M10-B247v 929 <0.5 >47, M10-B255v 1092 <0.5 46, M10-B258v , These dates suggest that recent warming is unique in >40,000 years. Alternate interpretations?

39 Barnes C dates on dead Penny veg from ~110 ice caps

40 Penny Ice Cap All old sites were above the Laurentide Ice Sheet so carried only local ice caps.

41 Mountain-top areas are all <0.2 km 2 limiting the maximum thickness of an ice cap to ~50 m

42 Current rate of ice-surface lowering m asl is ~0.5 m a years melts maximum ice thickness

43 Consequently, we can say with considerable confidence that summers of the past century were warmer on average than any century in at least 40,000 year.

44 14 C dates are at the edge of its range. Greenland ice cores provide context for when Earth might have been last even warmer than the early Holocene

45 d 18 O ( ) We speculate that the true age of our old veg is -31 NGRIP, Greenland ~120,000 years, at the end of the last interglaciation. d18o Age (years)

46 And what is the current snowline? 120,000 yrs Calibrated Years Ago

47 No ELA Penny Ice Cap NASA IceBridge lidar data: Penny Ice Cap snowline was everywhere above the ice cap: >1980 m asl

48 Current snowline measured by NASA overflights years of summertime cooling has now been reversed by a 4 C rise in recent decades

49 Conclusions 5000 years of cooling summers (2.5 C) has been reversed in recent decades; snowline has risen ~800 m (4 C summer warming), despite the continued decrease in solar energy Current summer temperatures are warmer on average than any century in >40,000 yrs, including peak warmth of the early Holocene when Arctic summer insolation was 10% greater than today.

50 Conclusions Our data from Arctic Canada cannot be explained by changes in solar forcing. They add additional evidence to the growing consensus that anthropogenic contributions to the atmosphere and strong positive feedbacks have now resulted in unprecedented recent Arctic summer warmth, well outside the range of natural climate variability.

Welcome to ATMS 111 Global Warming.

Welcome to ATMS 111 Global Warming http://www.atmos.washington.edu/2010q1/111 Isotopic Evidence 16 O isotopes "light 18 O isotopes "heavy" Evaporation favors light Rain favors heavy Cloud above ice is