Unit 4: Considering the Influence of Light and Thermal Phenomena on Global Clima
Unit 4: Considering the Influence of Light and Thermal Phenomena on Global Climate
VI. Using Central Ideas Based on Evidence to Consider the Impact of Global Climate Change
A. Exploring the impact of global climate change on sea levels
What is the evidence that sea levels are rising? Why is this happening? In particular, what happens when light from the Sun shines on snow and ice on land versus in open water? What happens when light from the Sun shines on the oceans?
Question 4.10 What evidence indicates that sea levels are rising?
The IPCC Fifth Assessment report on The Physical Science Basis devoted Chapter 13 to the topic of sea level change (pp.1137-1216). Figure 4.32 presents a line graph from this report. This graph represents past, recent, and predicted global average sea levels.
- What does the vertical axis represent?
- What does the horizontal axis represent?
- What do the lines represent?
- What does the shape of the lines imply about global average sea level?
The vertical axis represents the mean sea level in meters.
The horizontal axis represents time from 1700 to 2100.
The jagged lines represent the mean sea level based on various data. The smooth red and blue lines represent projections of mean sea level based on two different computer models of predicted greenhouse gas emissions.
The global mean sea level appears to have been relatively stable from about 1700 to about 1800 according to interpretations of layers evident in vertical cores removed from peat in salt marshes. The global mean sea level at about 1700 is taken to be the zero level to which later global mean sea levels are compared.
The global mean sea level appears to have begun rising slightly from about 1800 to about 1900 and continued rising at an increased rate from about 1900 to about 2000. The latter yearly mean sea levels were based on several different tide gauge studies, represented by different color lines, as well as from layers in cores of peat in salt marshes.
In 1993, satellite altimeter radar measurements began. (https://www.star.nesdis.noaa.gov/sod/lsa/SeaLevelRise/). Such highly accurate data can provide detailed information about the relative contributions by thermal expansion of the oceans and by melting ice in Greenland, Antarctica, and mountain glaciers elsewhere (https://sealevel.jpl.nasa.gov/documents/1596/?list=projects ). Dr. Anny Cazenave was a lead author in such satellite altimeter radar studies (https://blogs.ei.columbia.edu/2020/01/21/pioneer-in-spotting-modern-sea-level-rise-to-receive-2020-vetlesen-prize/).
The lines projecting mean sea level rise during the 21st century are based on two computer models that differ in the predicted concentration of carbon dioxide. These predictions depend upon actions taken, or not taken, to curb greenhouse gas emissions. These models are called Representative Concentration Pathways (RCPs). RCP2.6 (blue) models a scenario that assumed reduced emissions with an increase in average global temperature of less