December 2002 Section 2 Past Changes in Climate

Global surface temperatures are rising Relative to average temperature

However, developing reliable long term climate trends is a challenge that must deal with many sources of measurement error Ship data Automated buoys

1943 Annual adjustment = 1.1°C Effects of station relocations and other biases must be corrected Mont Joli, Quebec

Year D e g r e e s C Source: Peterson et al Rural Data Set (2290 Stations) Full Data Set (7280 Stations) Stations with large urbanization effects must be removed from the data base

Model studies suggest that SST corrections for systematic errors have significantly improved the quality of the record

Global mean combined land/ocean Temperature, including error margin Source: IPCC(2001)

On decadal time scales, surface and tropospheric behaviour can differ

Less so on multi-decadal times scales

Canadian temperatures have also increased substantially during the past decade

Changes in temperature are unevenly distributed Degrees C Trends for

Fall 2001 was the 18 th consecutive above normal season

Precipitation has increased in some parts of the world and decreased in others Trends (%/century) in annual precipitation for Insert figure

In many regions, changes in total precipitation are linked to changes in heavy precipitation

Canada is becoming wetter Percent change in precipitation

However, summers in some parts of North America have become much drier Summer Palmer Drought Severity trends for indicates 95% significance

Paleo records suggest dry periods have been common in central North America in the past Salinity Trends for Moon Lake, S.D. WET DRY

Water levels in the Great Lakes vary considerably, and are currently decreasing

Year Metres ASL Lake Ontario water levels are now less variable due to flow controls

John Walsh – U. Illinois Arctic spring snow cover has been declining rapidly Std. Anomaly for Feb-July relative to Year

Arctic sea ice has become much thinner

Arctic Ocean sea ice is becoming less extensive

The decline in sea ice extent is unprecedented in at least the past century Annual Mean

Arctic melt seasons are becoming longer Year Number of melt days

A variety of indicators show a changing Arctic climate 1998 is particularly unusual

Trends in heavy precipitation vary across Canada Fraction of annual precipitation falling in heavy events (%/yr) ºº

Canada is becoming “less cold” Trend in 5 th percentile of daily T min (Winters, ) = less extreme = more extreme X = statistically significant

Trend in number of cold spells (consecutive periods below 20 th percentile) -+ The number of cold spells are also decreasing

Trend in number of frost days ( ) The number of “frost days” are decreasing

El Nino - La Nina behaviour patterns have been changing

The frequency of intense North Atlantic hurricanes appears to vary considerably

Figure Year Northern Hemispheric intense winter storms appear to be occurring more frequently Storms per Winter

Changes in intense NH winter storms and temperatures correlate well

Coral data from south-central Pacific also show significant ocean warming

Monthly Average Salinity Anomalies at Ocean Station P The NE Pacific has become less saline

Trends in NH surface air temperatures appear to be linked to the Arctic Oscillation Index

The North Atlantic Oscillation Index is also linked to regional climates, and has increased Winter NAO

Winter North Atlantic wave heights have increased in the northeast and decreased at mid-latitudes Significant wave height trend pattern ( ) 1-3 cm/yr decrease 2-6 cm/yr increase

Physical and Ecological Systems around the world are beginning to change

Global costs of natural disasters are rising Insured losses (Constant US Dollars, 2000 values) Economic losses (Constant US Dollars, 2000 values) Trend of economic losses _____ Trend of insured losses Economic losses from great natural catastrophes worldwide

There has also been a 10-fold increase in North American natural disaster losses

Current NH temperatures are very unusual within at least the past 1000 years