MCC: Temperature and Measures of Climate Change
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
MCC: Temperature and Measures of Climate Change
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