Determining global temperature
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Dec 6, 2023
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Determining global temperature
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What challenges might a climate scientist encounter when calculating global temperature
from the available weather stations?
Spatial Coverage:
Some regions, especially remote areas like the Arctic, Antarctic, and parts of
Africa, might have fewer weather stations, leading to gaps in data. This lack of uniform
distribution can result in underrepresentation of certain areas, potentially skewing the global
average.
Data Consistency and Quality:
Since data is collected daily, there can be inconsistencies due to
equipment malfunctions, human errors, or station relocations. Additionally, older stations might
have used different methodologies or instruments than newer ones, leading to potential
discrepancies in the data over time.
Temporal Coverage:
Some stations might have longer historical records than others. A station
that's been active for 150 years will provide different insights than one that's been active for
just 20 years.
Urban Heat Island Effect:
Stations located in or near urban areas can record higher
temperatures due to human activities and infrastructure, which might not represent the
broader regional climate.
Temperature trends are most often reported as temperature anomalies. What is a
temperature anomaly?
A. A temperature anomaly is the reported temperature in degrees Celsius.
B. A temperature anomaly is an outlier - a very high or very low value that cannot be explained
in the record.
C. A temperature anomaly is the departure from the average temperature over a certain
comparison period called the "normal".
D. A temperature anomaly is synonymous with an average or mean, so you can have local,
regional, and global temperature anomalies.
What might you do to address the bias towards areas with more weather stations?
Weighted Averaging:
Instead of giving equal weight to each station, assign weights based on
the area they represent. For instance, a single station in a vast desert should have more weight
than one of many in a small urban area.
What are the steps to the gridded approach?
The approach used by climate lab researchers is to divide the earth into grid cells.
1.
Instead of using each weather station's data directly in the global average, the earth is
divided into a grid.
2.
For a given grid square or cell, records of all stations in the grid cell are averaged.
Revisiting our example pictured here, the grid cell covering 70 stations in the region
around Lake Erie and the southern part of Lake Huron is summarized by a single average.
The grid cell covering 4 stations in Northwestern China/ Western Mongolia is also
summarized by a single average.
3.
The global set of grid cell averages are averaged together to create the global
temperature record.
Describe the trend for the grid cell including the Klamath River.
As an example, this is the temperature record for the grid cell encompassing the Klamath River,
where the Yurok live. Since 2010, temperatures have been 1-2 degrees warmer than the 1961-
1990 mean, and 2-3 degrees warmer than temperatures of the early 1900s.
Investigate
London, Ontario
1.
What is on the x-axis and y-axis? Describe the graph.
x-axis is the time in years, y-axis is the mean temp 1969-1990 in C.
2.
Go to the Larger Annual or Seasonal Image. What is shown by the dashed line?
Dashed Line: In many climate graphs, a dashed line often represents a reference or
baseline, usually an average temperature over a specific period. Given your hint about
the 1961-1990 normal, it's likely this dashed line represents the average temperature or
"normal" for that period.
3.
How are the temperature anomalies (y axis) determined? Hint: The 1961-1990 normal is
used to do the calculation.
Temperature Anomalies: Temperature anomalies are typically determined by taking the
difference between the temperature of a particular year (or month) and the average
temperature of a reference period (in this case, 1961-1990). If the temperature of a
given year is above this reference average, the anomaly is positive; if below, it's negative.
4.
What is the black solid line running through the data starting at 1860 and running to
2010?
Black Solid Line: This is likely a trend line, often used to depict the general direction or
trend of the data over time. Given its starting point in 1860 and ending in 2010, it likely
represents the overall temperature trend for this period.
5.
What trends do you observe? How much warming has occurred in this grid cell?
Trends: From the images (though it's challenging without the precise scale), it appears
there's a general upward trend in temperatures, indicating warming. The exact amount
of warming would require numerical data or a clearer scale.
6.
What are the steps involved to determine the grid cell temperature changes?
Gathering temperature data for each year or month within the grid cell.
Averaging the temperatures over a reference period (like 1961-1990) to get a baseline or
"normal."
Calculating the difference between the temperature of each year (or month) and the
baseline to get the anomaly for that year.
Plotting these anomalies over time to visualize changes.
Florida, USA
1.
How far back does the record go?
1850-1860 stopped, restart 1880 to recent.
2.
What is the main trend you observe?
observed is an upward trend,1980 rapid up, temperature anomalies or changes, mean
the region has been experiencing warming over the decades.
3.
How much warming has occurred in this grid cell?
4.
How does this compare to the grid cell where London, Ontario is located?
Similarly, 1980 rapid up
Moosonee, Ontario
1.
What trends do you observe?
How do the trends compare to the London grid cell?
The graph shows a clear upward trend over time, which indicates a rise in temperature.
There appear to be periodic fluctuations, which is typical for climatic data due to natural
variability. However, the overarching trend is a noticeable increase in temperature over
the years.
2.
Have a look at the temperature data for the Moosonee weather station (below).
Compared to nearby grid cells, the record is quite long. Why would Moosonee have such
a long record?
Transportation Hub: It could have been a hub for transportation, especially if it was a key
point for trains, boats, or later, airplanes. Transportation hubs often have weather
stations due to the significance of weather information for safe transit.
Arctic Bay, Baffin Island, Nunavut
1.
What are the main trends you observe in the grid cell data.
How does it compare to
Moosonee and London?
2.
How much warming has occurred in this grid cell?
How does this compare to London?
Grid cell of your choice
1.
Describe the overall trend.
2.
How long is the record? Are you surprised by how long or short it is?
3.
How much warming or cooling has occurred?
4.
How does it compare to the grid cell that includes London, Ontario? Can you explain the
differences or similarities?
About this animated map
How widespread are areas of cooling?
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Areas of cooling appear to be less dominant than areas of warming. While the exact regions are
hard to pinpoint without interacting directly with the map, there seem to be some cooler
regions in parts of the Southern Hemisphere and possibly some isolated areas in the Northern
Hemisphere.
How widespread are areas of warming?
Areas of warming are notably more widespread than cooling. Significant portions of the map,
especially in the Northern Hemisphere, display warmer colors, indicating temperature
anomalies on the positive side.
Which areas have warmed the most?
The most intense warming (indicated by the darkest shades on the map) seems to be
concentrated in parts of the Arctic and some regions in the Northern Hemisphere. The Arctic's
pronounced warming is consistent with observations of accelerated warming in polar regions
due to the feedback mechanisms present there.