CLIMATE CHANGE, CATASTROPHE AND THE TIDES OF HISTORY. 1. CLIMATE THE LONG VIEW.

Transcription

1 LL Innis / 3ALB 2018 CLIMATE CHANGE, CATASTROPHE AND THE TIDES OF HISTORY. 1. CLIMATE THE LONG VIEW.

2

3 Climate has controlled our evolution, our spread around the globe, and our social, political, economic and cultural development. Civilization may have improved our material condition, but it s made us more not less dependent on the vicissitudes of climate.

4 We are being constantly reminded of the danger that global warming poses, but demonstrating simple cause and effect relationships is difficult. In part, that s due to climatic variability ( noise ). For example, our recent hot, humid spell and the host of new temperature records here and across the globe would seem to support the premise of global warming, but what about the very cold period we had last winter? Are these two extreme events incompatible?

5

6

7 Winter 2018 January 13

8 The simple answer is NO. They are both part of a very complicated package. What s in that package? Increasing mean global temperature. Increasing extremes of weather more hot and cold episodes. Increasing storminess(more tornadoes, hurricanes, etc.). Changes in the character of large-scale circulation systems (El Nino, etc.).

9 We need to remember that not all climate change is large and long term. Small shifts, even individual events (a hurricane, a drought, a late killing frost, etc.) may have huge societal consequences. Consequences may be complicated.

10 Combined effects of Typhoon Jebi and a 6.6 magnitude earthquake in Hokkaido. Sept. 5, 2018.

11

12 We focus on warming because we can demonstrate that it is happening and that we are largely responsible for it was the warmest year since reliable records have been kept (1880). 16 of the 17 warmest years on record occurred since is well on the way to being on that list!

13 Recent temperature changes. Note the large interannual variability.

14

15 Lacking in most of the reporting on global climate change is perspective. What have past global climates been like? How do we know? What causes climate change? Why should we be concerned?

16 Climate has been changing since Earth developed a crust some 4 billion years ago. For most of Earth history, climate has been much warmer than it is today although it seems to fluctuate from hothouse to icehouse. At times the Earth may have been entirely ice covered (Snowball Earth).

17 Our impact on mean global temperature appears to be about C, but the rate is not slowing down. Models predict up to 5C warming by These values may seem small, but they will have huge consequences. One already noticeable consequence is rising global sea level.

18 Another is food production.

19 Before we go any further, let s take a quick look at climate through Earth history.

20 Temperature changes over the last 2000 years.

21 Changes through the Holocene

22 Changes through the Tertiary and Quaternary- the last 65 million years.

23 600 million years of temperature change

24 So how do we reconstruct past climates and how can we date the changes? For the last few hundred years we have instrumental measurements and, more recently, satellite imagery. Beyond that we have to use proxy indicators; data that document change without directly measuring it.

25 Weather instruments and networks; Temperature from the early 18C Fahrenheit, Pressure (barometer) Torricelli, Precipitation (rain gauge) Wren, Humidity (hygrometer) Folli, Wind (anemometer) Alberti, 1450.

26 Modern data collection; Most weather data are routinely and (mostly) automatically collected at weather stations. These standard measurements are for temperature, precipitation, wind speed and direction, humidity, solar radiation. There are about 1500 semi-permanent weather stations in Canada. About 500 of these satisfy WMO standards. Longest record? U of T since Our nearest station is located at Burlington Piers ( CCIW by the lift bridge).

27 Standard meteorological station

28 The record can be extended into the recent past by the use of historical proxy data. These include ships logs, factors logs for Hudson Bay posts, cherry blossom blooming dates in Japan, rogations for rain, sea ice measurements, etc.

29 Extending the record to the distant past. Let s look at a few of the methods; Tree rings. Pollen analysis. Ice cores. Sedimentary rocks.

30

31 Tree Rings (dendroecology/dendrochronology/ dendroclimatology)

32 Bristlecone pine oldest living tree is 5067 years old.

33 Niagara Escarpment white cedars oldest living tree is 1367 years old.

34 Pollen analysis. Crawford Lake is meromictic and varved.

35 Pollen record from Crawford Lake a climatic record (trees) and a human impact record (herbs).

36 Ice cores. Sites in Greenland and Antarctica. Oldest record is 800,000 years (EPICA/Dome C)

37 Reconstructed temperatures from Antarctic ice cores and dust measurements.

38 Sedimentary rocks. They provide a record for nearly 4 billion years. The record is mostly marine. Why? It reflects (a) past plant and animal life through fossils, (b) the environments of deposition. So rocks can provide information on both climate and past geographies.

39 Stromatolites (blue-green algae colonies) have been around since life evolved.

40 Corals past and present.

41 Stratigraphy of Southern Ontario. Depositional environments.

42 Evaporites in Southern Ontario. Halite (rock salt) and gypsum. The Goderich salt mine (below).

43 For most of the Ordovician and Silurian ( million years ago) North America was mostly underwater and equatorial in location.

44 Fossil glacial till (Gowganda tillite). Fossil sand dunes (bottom left). Forest beds on Axel Heiberg Island (below).

45 Dating climatic change events. 1. Relative Dating (a) relative age determined by stratigraphic position usually layers higher in a sequence are younger than those below, (b) relative age determined by the presence of index fossils. These are fossils with a broad geographic range, but with a limited time range.

46

47 Trilobite (below) Graptolites (bottom)

48 2. Absolute Dating. (a) Sediments with annual growth rings (tree rings, varves, coral growth, speleothems, etc.).

49 (b) Radiometric dating. Various techniques involve the measurement of changes in isotopic composition through time. The most important for us are radiocarbon dating which measures the ratio between 12C and 14C, and Potassium-Argon (K-Ar) dating.

50 Radiocarbon dating is useful up to 40,000 years, but can be extended by AMS (accelerator mass spectrometry). K-Ar dating can be used through the entire geologic record.

51 So we ve seen that Earth s climate is constantly changing. Some of those changes appear to be random and others may be cyclical. It s clear that until now, naturally induced changes have been far larger than those that we have contributed. What determines global climate? We ll find out next week!