2.1: Temperature Anomalies

• Temperature can vary drastically over short distances as the local environs change

  • Eg. Areas with large amounts of concrete tend to be warmer than areas with lots of vegetation

• Measuring absolute temperature requires extensive thermometer networks

  • Since this is impractical, scientists record temperature anomalies

  • Temperature anomaly: the difference between absolute temperature and a reference temperature

• Scientists have calculated that roughly 100 thermometers distributed around the globe are needed to calculate the global temperature anomaly

2.2 Recent Climate Change

Surface Thermometer Record

• Sufficient coverage of Earth’s surface has allowed scientists to estimate the global average temperature anomaly since the mid-1800’s

  • The data show that the Earth has warmed by 1.10˚C in that time, which is significant

• The warming has not been uniform in time (little warming from 1940-1975)

• Despite short-term variability, the warming since the 1970’s is essentially continuous

  • Each decade is warmer than the last

• Warming is occurring nearly everywhere → "global” warming

  • Land areas warm more than oceans

  • The northern hemisphere is warming faster than the South

    • Most people live on land in the northern hemisphere, so this poses great risk to the human population

• The thermometer network was not designed for climate monitoring and has changed significantly over the years

  • Eg. changing types of thermometers, station location and environment, observing practices, and other sundry alterations

• Don’t rely solely on this data set to form conclusions about climate change

Satellite Measurements of Temperature

• Global temperature can be measured from orbit, and the US has used instruments on satellites to measure this since 1978

  • These data show a warming trend with an average increase of 0.13˚C per decade

• Satellite measures of temperature have their own disadvantages

  • Satellites actually measure the average temperature of the lowest 8km of the atmosphere, not the Earth’s surface temperature

  • Satellites move slightly in their orbit, so they pass over certain places at later times in the day as years pass; thus, a reading might have been at 2pm one year and 3pm the next, and increased because of that rather than a climate change-related increase

    • This must be identified and adjusted for

  • Satellite instruments can be mis-calibrated

  • The short time span of the satellite record must also be taken into consideration

    • Both of these issues (mis-calibration and time span) are accounted for

• These issues is why it’s important to compare satellite measurements to surface thermometer records

Ice

• Ice is a dependable indicator of temperature as it always melts at 0˚C

• This can be used to check the accuracy of other indicators of warming temperatures

Glaciers

• Glaciers form in cold regions when snow falling in the winter doesn’t melt completely

• As snow accumulates, the snow at the bottom becomes compacted by the weight of the overlying snow and turns into ice

  • This eventually produces glaciers that are hundreds or even thousands of feet thick

Sea Ice

• Sea water freezes to form a layer of ice floating on top of the ocean in polar regions

  • The area of see covered by sea ice varies throughout the year

  • Due to climate change, this area has decreased and the ice that remains has become thinner

Ice Sheets

• Very large glaciers

  • Major northern hemisphere ice sheet: Greenland

  • Major southern hemisphere ice sheet: Antarctica

• Scientists can measure changes in the mass of ice sheets by measuring changes in the sheets’ height using space- and aircraft-borne laser altimetry or by measuring how the sheets alter the Earth’s gravity

Ocean Temperatures

• Much of the heat trapped by greenhouse gases goes into heating the oceans, so examining the warming of the oceans is also an important facet of climate change research

  • The ocean temperature is not the temperature of the ocean’s surface, but the average temperature of its depths

  • The average depth of the ocean is 4km

• The temperature of its depths are measured by scientists lowering thermometers to various depths and recording the temperatures

• The ocean is observed to have been warming

• While the ocean is warming less than land, water holds lots of energy, so seemingly small increases in temperature represent an enormous accumulation of energy in the climate system

Sea Level

• One way that the change in sea level is related to climate change is the melting of grounded ice

  • Grounded ice: ice that rests on land

• When grounded ice melts and water runs into the ocean, the total amount of water in the ocean increases and sea level rises

  • This is different from the melting of floating ice as it changes the sea level rather than just having existing water in the ocean shift between forms of matter

• Water expands when it warms, and as ocean is warming, this thermal expansion will also raise sea levels

• From 1900 to 2018, the average global sea level (or global mean sea level) rose by 0.19m, the average rate of sea level rise being 1.6mm/year

  • This is faster than any century for the past 3,000 years

• From 1993 to 2019, the rate of increase was 3.2 mm/year

  • Sea levels are rising at a faster and faster pace as time passes

Is Today’s Climate Changing?

• Yes.

• The evidence supporting climate change is so strong that the Intergovernmental Panel on Climate Change (IPCC) describes global warming as “unequivocal”

• Results have been replicated time and time again and is one of the most replicated conclusions in scientific history

  • Surface thermometer records, satellite records, the loss of ice in the oceans, the rising sea levels, and the increased heat content of the sea all support the warming climate

  • Each of these data sets is also fundamentally independent

• In addition to these scientific figures, there are thousands of observed physical, biological, and ecological changes that are consistent with warming

• Contrary data sets are rare, regionally limited, and vastly outnumbered by evidence of warming

What Is Not Evidence of Climate Change

• Climate change is a shift of statistics in the atmosphere; thus, individual events are rarely indicative of entire climactic change

• It is more effective to examine statistics and figures of the environment that have been recorded over longer periods of time to identify patterns and shifts