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
• 
• 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
    *
    * 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