1. Chapter 2: Weather, Climate, Climate Variability, and Climate Change
Protecting our Health from Climate Change: a Training Course for Public Health Professionals
Chapter 2: Weather, Climate, Climate Variability, and Climate Change

2. Overview: This Module Define terms
Discusses climate change and how has it been determined that humans are influencing the climate
Shows some of the climatic changes that have occurred to date
Shows how climate change will affect the weather for decades to centuries

3. Weather, Climate, Climate Variability, and Climate Change
Definitions
The greenhouse effect
Detection and attribution of climate change
What changes have occurred
What changes are projected
This presentation will provide definitions of weather, climate, climate variability, and climate change. We’ll review the greenhouse effect, then talk about the detection and attribution of climate change. 3

4. Definitions Climate is what you expect Climate variability
Based on 30-year averages
Weather is what we experience day-to-day
Climate variability
Short-term fluctuations around the average weather
Includes ENSO (El Nino-Southern Oscillation)
Climate change
Operates over decades or longer
General circulation models (GCMs)
Scenarios, not predictions
The climate in a particular location is defined as the 30-year averages of weather variables, such as temperature and precipitation. Most of the research on the health impacts of climate variability and change uses the period as the climate baseline. Climate scientists analyze data against this baseline.
Weather is what we experience day-to-day.
Climate variability includes short-term fluctuations around the average weather, such as the El Nino Southern Oscillation (ENSO).
Climate change operates over decades or longer and is projected using increasingly sophisticated earth system models (ESMs). It is important to understand that these models are based on scenarios (or plausible futures) of how many people there will be in the world, where they will live, how wealthy they will be, etc. These scenarios project emissions of greenhouse gases. These emission concentrations are then input into the ESMs to project possible future climate. ESMs do not predict what will occur; they project how temperature and precipitation could change under different assumptions of greenhouse gas emissions. 4

5. Radiation from the sun passes through Earth’s atmosphere to the surface. Most of the radiation is absorbed, which warms the Earth. The Earth and atmosphere reflect some radiation back out to space. Some of this radiation hits greenhouse gas molecules in the atmosphere (greenhouse gases include water vapour, carbon dioxide (CO2), methane, nitrous oxide, halocarbons, and ozone) that absorb the radiation and re-emit it. The effect of this is to further warm the Earth’s surface and lower atmosphere. The greenhouse effect is critical to life on earth; without it, the Earth would be 33ºC colder than present and the diurnal temperature range would increase dramatically.
An important issue for understanding the potential impacts of climate change is the long lifetime of greenhouse gases in the atmosphere. CO2 can take more than 100 years to come to equilibrium once it is emitted. Thus, the Earth is committed to several decades of climate change after stabilization of greenhouse gas emissions is achieved, and sea level will continue to rise for more than 1,000 years as the ocean continue to warm because of the processes involved in stabilization.
IPCC 2007a 5

6. Global Temperature Variations on Three Time Scales
Last million years
Last 10,000 years
These panels show the degree of climate change over different temporal scales. In all three panels, the doted line is the global average surface temperature.
The top panel shows global average surface temperature from 1,000,000 years before present to the present (the right edge of the panel). The high degree of variability in global temperature is clear. Historically, the global average surface temperature was rarely as warm as it was in the 1980s; surface temperatures have increased since then.
The middle panel shows global average surface temperature from 10,000 years before present to the present (the right edge of the panel). The warming at the end of the last ice age is shown at the left edge.
The lower panel shows global average surface temperatures from 1,000 years before present to the present (the right edge of the panel). Both the Little Ice Age and Medieval Warm Period are shown.
Comparing the top and lower panels shows that the Earth’s climate has been relatively warm and stable for the past 10,000 years compared with earlier periods; it was during this period that much of human society has developed.
Last 1,000 years
Folland et al. 1990 6

7. Temperature over Greenland over Past 17,000 Years
Ice cores taken in Greenland show how temperatures changed from 17,000 years before present to the present (the right hand edge of the panel).
Again, this graph shows that temperatures have been relatively warm and stable over the past 10,000 years compared with previous periods. The Medieval Warm Period and Little Ice Age, both of which had important impacts on crop yields, and therefore human societies, are small variations compared with earlier variability. The Younger Dryas was a period of sudden cooling as the Earth was warming out of the last ice age. Temperatures dropped significantly over a few decades. Warming out of the Younger Dryas also was rapid. The causes of this event are under investigation.
Alley 2000 7

8. 1,000 Years of Changes in Carbon Emissions, CO2 Concentrations, and Temperature
The three graphs on this chart show changes over the past 1,000 years. The bottom graph shows carbon emissions; the beige band shows emissions due to change in land use (such as deforestation to create agricultural land) and the pink band shows fossil fuel emissions. Fossil fuel emissions have increased dramatically since the Industrial Revolution.
The middle, beige graph shows increasing atmospheric CO2 concentrations in response to increasing carbon emissions. The atmospheric concentration of CO2 prior to the Industrial Revolution was approximately 280 ppm; the current concentration is nearing 390 ppm. This concentration has not been exceeded during the past 420,000 years and probably not during the past 20 million years.
The pink line shows that, although there has been variability, global average surface temperature has paralleled CO2 concentrations for the past 1,000 years. The global average surface temperature increased approximately 0.7ºC during the past century, with about 0.4ºC of that increase since the 1970s. Temperatures are now changing at 0.18ºC per decade. Surface temperatures now exceed the upper limit of natural (historic) variability. 8

9. Instruments, such as thermometers and rain gauges, have been recording temperature, precipitation, snow cover, and other variables since the 1860s. These three panels from the IPCC 4th Assessment Report (IPCC, 2007a) show changes in the global average surface temperature, global average sea level, and Northern Hemisphere snow cover for March-April over this time period, compared with the climate baseline. Smoothed curves represent decadal averaged values and circles show yearly values. The shaded areas are the uncertainty intervals estimated from a comprehensive analysis of known uncertainties.
Temperature and sea level have increased, while snow cover has decreased. In the top panel, one can see that the rate of temperature increase has been accelerating in recent decades.
IPCC 2007a 9

10. The top figure shows patterns of linear global temperature trends over the period 1979 to 2005 estimated at the surface (left), and for the troposphere from satellite records (right). Grey indicates areas with incomplete data.
The bottom figure shows annual global mean temperatures (black dots) with linear fits to the data. The left hand axis shows temperature anomalies relative to the 1961 to 1990 average and the right hand axis shows estimated actual temperatures, both in °C. Linear trends are shown for the last 25 (yellow), 50 (orange), 100 (magenta) and 150 years (red). The smooth blue curve shows decadal variations, with the decadal 90% error range shown as a pale blue band about that line. The total temperature increase from the period 1850 to 1899 to the period 2001 to 2005 is 0.76°C ± 0.19°C.
IPCC 2007b 10

11. Given that records show that climate is changing, the next question is the degree to which human activities are responsible.
The top figure shows global mean surface temperature anomalies relative to the period 1901 to 1950, as observed (black line) and from models that included anthropogenic and natural forcings. The thick red curve shows the means from the models and the thin lighter red curves show the individual model results. Vertical grey lines indicate the timing of major volcanic events.
The bottom figure shows global mean surface temperature anomalies relative to the period 1901 to 1950, as observed (black line) and from models that included only natural forcings. The thick blue curve shows the means from the models and the thin lighter blue curves show individual model results.
IPCC 2007b 11

12. Global and Continental Temperature Change
This figure shows similar results, but on finer scales: for all continents, global average surface temperature, global average surface temperature over land, and global average surface temperature over the oceans. The black line in each box is average surface temperature as measured over the period , plotted against the center of the decade and relative to the corresponding average for the period The blue bands are the results (5-95%) from running climate models using only factors known to affect temperature (volcanoes and sun activity); no anthropogenic emissions were included (i.e. deforestation and burning of fossil fuels). The red bands are the results from running climate models with both natural and anthropogenic factors.
It can be seen that models run using only natural forcings match historic data reasonably well until about the 1970s, and can not explain observed climate changes since then. Including anthropogenic activities is required to explain observations over the past 30+ years.
IPCC 2007b 12

13. Concentrations of Greenhouse Gases over the Last 10,000 Years
The human activities that emit greenhouse gases are contributing to climate change. These three graphs show atmospheric concentrations of CO2, methane, and nitrous oxide over the last 10,000 years (large panels) and since 1750 (inset panels). Measurements are shown from ice cores (symbols with different colors for different studies) and atmospheric samples (red lines). The corresponding radiative forcings (a measure of how much the gas influences the global climate) are shown on the right hand axes of the large panels.
All three graphs show dramatic increases in emissions starting around the Industrial Revolution.
IPCC 2007b 13

14. Concentrations of Greenhouse Gases in the Past 2,000 Years
This graph shows the concentrations of CO2, methane, and nitrous oxide over the past 2,000 years.
IPCC 2007b 14

15. Atmospheric CO2 Concentration and Temperature Change
Projected concentrations
of CO2 during the 21st century are 2-4 times pre-industrial levels
Atmospheric concentrations of CO2 are projected to rise 2- to 4-fold over pre-industrial concentrations this century, with global surface temperature projected to increase about 2 to 6ºC by the end of the century. This temperature change will happen in 100 years, instead of the 15,000 years since the last ice age. Although the temperature change may not sound like much, but the difference in global mean surface temperature between now and the last ice age is close to the upper range. Further, the long lifetimes of CO2 (approximately 100 years) and other greenhouse gases in the atmosphere means that climate change will continue for several decades after stabilization of greenhouse gas emissions; sea level rise will continue for at least 1,000 years.
What might be the consequences of these changes in CO2 concentrations? 15

16. Global Average Surface Temperature
This figure from the IPCC 4th Assessment Report shows increases in global average surface temperature from 1900 to 2000, and projected increases to 2100 under different scenarios of how many people there will be in the world, how wealthy they will be, etc. Two issues of note. The yellow line shows the “climate change commitment” – this is how much climate change the world is committed to because of the greenhouse gases (and deforestation) already emitted. Global average surface temperatures will rise at least another 0.5°C no matter what actions are taken. The other lines show projected changes under different scenarios. Which pathway is followed will be based on human decisions over the next few decades.
IPCC 2007b 16

17. Surface Temperature Anomalies
Similar to an earlier figure, this shows the observed decadal mean continental surface temperature anomalies (°C) for the period 1906 to 2005 and the projections for 2001 to Anomalies are calculated from the 1901 to 1950 average. The black lines represent the observations and the pink and blue bands show modeled average temperature anomalies. The yellow shading is the 5th to 95th percentile range of projected changes according to the SRES (Standardized Reference Emission Scenarios; these describe how world demographics and economies might change over the next century) A1B emissions scenario. The green bar is the 5th to 95th percentile range of decadal mean anomalies from the 20th-century simulations with only natural forcings.
IPCC 2007b 17

18. Projected Surface Temperatures
These figures and maps show projected surface temperature changes for the early and late 21st century relative to the period 1980 to The central and right panels show average projections (°C) for thee different scenarios averaged over the decades 2020 to 2029 (center) and 2090 to 2099 (right). The left panel shows corresponding uncertainties as the relative probabilities of estimated global average warming from several different studies for the same periods.
IPCC 2007b 18

19. Land Areas Warm More than the Oceans with the Greatest Warming at High Latitudes
This shows in more detail the geographic differences in warming.
Annual mean temperature change, 2071 to 2100 relative to Global average in 2085 = 3.1°C.
IPCC 2007b 19

20. Effect of Extreme Temperatures When the Mean Temperature Increases
The schematic shows the effect on extreme temperatures when the mean temperature increases, for a normal temperature distribution. If both the mean and variance of temperature change, then there could be a larger increase in record hot weather.
IPCC 2007b 20

21. Observed, Modeled, and Projected Precipitation
These maps show spatial patterns of observed (top row) and modeled mean (middle row) seasonal mean precipitation rate (mm day–1) for the period 1979 to 1993, and the projected mean changes by the period 2090 to 2099 relative to 1980 to 1999 (% change) based on the SRES A1B scenario (bottom row). December to February means are in the left column, and June to August means are in the right column. In the bottom panel, changes are plotted only where more than 66% of the models agree on the sign of the change. The stippling indicates areas where more than 90% of the models agree on the sign of the change.
In summary, many of the wet areas of the world are projected to get wetter (increased precipitation), while many of the dry areas of the world are projected to become drier.
IPCC 2007b 21

22. Some Areas are Projected to Become Wetter, Others Drier
This map shows in more geographic detail changes in mean precipitation.
Annual mean precipitation change: 2071 to 2100 relative to 1990.
IPCC 2007b 22

23. The map on top shows observed trends (% per decade) over the period 1951 to 2003 in the contribution to total annual precipitation from very wet days (i.e. > 95thile). White land areas have insufficient data for trend determination.
The both graph shows anomalies (%) of the global (regions with data shown in top panel) annual time series of very wet days (with respect to ) defined as the percentage change from the base period average (22.5%). The smooth orange curve shows decadal variations. The large increase in anomalies since 1990 is obvious.
IPCC 2007b 23

24. Palmer Drought Severity Index
The map and figure show the monthly Palmer Drought Severity Index (PDSI) for 1900 to The PDSI is a prominent index of drought and measures the cumulative deficit (relative to local mean conditions) in surface land moisture. The lower panel shows how the sign and strength of this pattern has changed since Red and orange areas are drier than average and blue and green areas are wetter than average, based on the trend shown in the lower curve. The smooth black curve shows decadal variations.
The map shows the widespread African drought, especially in the Sahel, and areas that have become wetter, especially in eastern North and South America and northern Eurasia.
IPCC 2007b 24

25. Recent Trends in Climate Sensitive Indicators
These graphs show decreasing sea ice, snow cover, glacier extent, etc. Decreasing glacier extent will have implications for freshwater availability in many parts of South East Asia.
Details:
Anomaly time series (departure from the long-term mean) of polar surface air temperature (A, G), arctic and Antarctic sea ice extent (B, F), Northern Hemisphere (NH) frozen ground extent (C), NH snow cover extent (D), and global glacier mass balance (E). The solid red line in E denotes the cumulative global glacier mass balance; in the other panels it shows decadal variations.
IPCC 2007b 25

26. Tropical Atlantic Sea Surface Temperature Anomalies (oC)
Hurricanes draw their strength from temperature of the ocean. As shown in this figure, tropical Atlantic (10°N-20°N) sea surface temperature annual anomalies (°C) in the region of Atlantic hurricane formation, relative to the 1961 to 1990 mean, have increased in the last two decades.
IPCC 2007b 26

27. Sea Level Rise
The figure shows time series of historic global mean sea level (deviation from the mean and projected changes to For the period before 1870, global measurements of sea level are not available. The grey shading shows the uncertainty in the estimated long-term rate of sea level change. The red line is a reconstruction of global mean sea level from tide gauges, and the red shading denotes the range of variations from a smooth curve. The green line shows global mean sea level observed from satellite altimetry. The blue shading represents the range of model projections for the SRES A1B scenario for the 21st century, relative to the 1980 to 1999 mean. Beyond 2100, the projections are increasingly dependent on the emissions scenario.
IPCC 2007b 27

28. IPCC (2007b) Conclusions IPCC 2007b
This summarizes the conclusions of the IPCC on observed and projected trends in various climatic events. These changes could have significant impacts on human health.
An asterisk in column D indicates that formal detection and attribution studies were used, along with expert judgment, to assess the likelihood of a discernible human influence.
Source: IPCC (2007b).
IPCC 2007b 28

29. This figures summarizes the conclusions of the IPCC 4th Assessment Report in terms of impacts of increasing temperatures, by degree and by decade. The impacts noted for 1°C can not be avoided because of the inertia in the climate system.
Recommended reading: IPCC 2007 report, WORKING Group II, Summary, pages 7 to 22 and page 25. 29