1.2: Is The Climate Changing?

Global Temperature Rise

• The overall trend of increasing temperatures can be seen from multiple agencies from different parts of the world

  

NASA’s Temperature Record

• NASA has kept record of annual average temperature since 1880 and found that 2022 was the fifth-hottest year on record

• The Goddard Institute for Space Studies (GISS) records Earth’s surface temperature (GISTEMP)

  • This shows a clear increase in Earth’s temperature
  • GISTEMP collects records from weather stations, Antarctic research stations, ships, and ocean buoys around the world

• Their work is verified through comparing data with organizations such as the National Oceanic and Atmospheric Association (NOAA)

• NASA also checks work with their own satellites orbiting the Earth and obtaining atmospheric readings

• All of the evidence that NASA and other organizations have collected asserts that Earth’s climate is warming

  

• The red/orange/yellow areas indicate overall warming, though some areas have cooled

• Land areas warmed more than the ocean

• Polar regions saw the most significant increase in temperatures

Shrinking Glaciers

• Glacier: a permanent body of ice that forms where climates are cool enough to maintain snow all year long

  • Most often found at high altitudes in the mountains and high latitudes in polar regions

• Glaciers form when fresh snow lands on a ground surface; due to the cold temperatures, it does not fully melt over the course of a year. The next year another layer of snow will be deposited on top.

• Over time the snowflakes lose their edges and the snow becomes more tightly packed.

• With further burial, the snow transforms into a packed granular material called firn

• As layers of snow accumulate, the weight compresses the lower layers into glacial ice.

  

• Rising global temperatures increase the melting rate of glacial ice

  • If the melting rate becomes faster than the rate of snow accumulation, it results in a net loss of ice
  • Over time, this can lead to a dramatic retreat or shrinking of glaciers
  • This is a trend that has been observed in glaciers worldwide; the most dramatic changes are observed in places where the warming has been the greatest

Greenland and Antarctica

• Earth’s two major ice sheets (continental glaciers) are located in the polar regions
  • North: Greenland
  • South: Antarctica
• NASA/German Aerospace CenterGravity Recovery and Climate Experiment (GRACE) satellites found that between 2002 and 2016, Greenland shed ~280 gigatons of ice/year and Antarctica shed ~125 gigatons of ice/year

Declining Arctic Sea Ice

• Not all ice on Earth is on land
  • Large areas of ocean that are in polar climates freeze due to the cold temperatures and form a layer of ice covering the ocean: sea ice
• A decline in Arctic sea ice over the last several decades has led to significant impacts on the Earth’s climate as a whole and the lives of the animals who live in the Arctic

Ocean Temperatures

• The ocean temperature is increasing, but at a slower rate than land temperatures
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• Due to water’s high heat capacity, an increase in ocean temperature (even a small one) indicates a large amount of extra energy that Earth has absorbed

Changes in Sea Level

• From 1901-2010, the average rate of sea level rise was 1.7 mm/year; global sea level is now rising 3.4 mm/year
  • Sea level is not just rising, the rate of increase is accelerating
• Warming will accelerate this trend by:
  • Thermal expansion of seawater — as water temperature increases, water expands and occupies more space
  • Increased melting of land ice — extra water added to the ocean from the melting of ice sheets on land
  • When ice on land melts, that water drains to the ocean, thereby adding more water to the basin
  • This causes an increase in sea level
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  • When the sea level rises, this causes the shoreline to shift landward
  • This change will affect coasts differently based on the topography and landforms at each location
  • Areas like the west coast of the U.S. have a mountainous coast and will be less affected by rising seas than areas on the east coast of the U.S. that have a very low coast such as Florida
  • Only melting land ice (not melting sea ice) is important when it comes to the issue of rising sea level
  • Displacement: sea ice is in the water, so its volume is already taken into account by the level of the ocean
  • Similar to ice cubes in a glass; when the ice melts, the level of water in the glass remains unchanged because the ice displaces an equal volume of water
  • Melting land ice is different as this is introducing more water to the system and thereby increases the water level, similar to pouring more water into a glass
  • Though not impacting sea level, melting sea ice still has significant negative consequences

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