An underestimation of sea level rise and climate change…


In a recent publication from the University of Hawai’i Manoa, researchers have found that long-standing records of historical ocean water levels do not match up with contemporary rates of sea level rise.

Dr. Philip Thompson in the School of Ocean and Earth Science (SOEST) states:

“It’s not that there’s something wrong with the instruments or the data, but for a variety of reasons, sea level does not change at the same pace everywhere at the same time. As it turns out, our best historical sea level records tend to be located where past sea level rise was most likely less than the true global average.”

Interestingly enough, locations where ice melting occurs create “ice melt fingerprints” that, when combined with Earth’s rotation and gravity, causes localized anomalies in sea level change that may not be as dramatically observed elsewhere. Global average sea level has typically increased about 3 millimeters (0.1 in) per year in recent decades, however it is important to note that global averages do not necessarily reflect rates of change in certain anomalous areas.


Sea level average change over the last 10 years. Although the global average is around 3 mm (0.1 in) per year, in certain anomalous areas around the globe, that rate may exceed 15 mm (0.5 in) per year.

The study concluded that previous rates of global average sea level rise are likely lower than actual rates. Sea level rise depends on the amount of global warming that occurs, which in turn depends on future levels of greenhouse gases.

nz215Last month, climate science reached an unfortunate milestone: the levels of carbon dioxide (an important greenhouse gas) in the atmosphere peaked above the symbolic figure of 400 ppm (parts per million). Scientists have designated 400 ppm as a threshold to avoid global warming temperatures of more than 2 degrees Celsius (3.6 degrees Fahrenheit), on average.

The Earth’s atmospheric carbon dioxide levels are in a balance between two major biological processes: plant photosynthesis (which takes up carbon dioxide and creates oxygen) and respiration (which creates carbon dioxide). All plants, from marine algae to conifer trees, photosynthesize. Pretty much every other living being respires. This dichotomy can be seen in atmospheric data readings over the course of the year (shown below, inset) as an ‘inhale’ and ‘exhale’ cycle; during the productive summer months, plants take out large amounts of carbon dioxide from the atmosphere. During the winter months, respiration is greater than photosynthesis, causing carbon dioxide to increase. September is usually the lowest month for carbon dioxide emissions, as it is the peak for plant photosynthesis, globally. These yearly fluctuations are normal responses to biological processes, however greenhouse gas emissions from human sources have driven this natural cycle above the threshold of 400 ppm, even in what is supposed to be the lowest month for carbon dioxide levels.


Trends in atmospheric carbon dioxide levels, taken from Mauna Loa Observatory in Hawai’i. Greenhouse gases are causing an increase in carbon dioxide levels at a higher rate than historical levels. Annual fluctuations in carbon dioxide are shown inset, with the lowest levels typically recorded in the month of September.

The Intergovernmental Panel on Climate Change (IPCC) expects a 0.5-1.0 meter sea level change by the year 2100, based on trends in global warming.Lifeline to climate refugees.jpg

The economic, social, and cultural impact of sea level rise will affect the lives of hundreds of millions of people worldwide. Already, ‘climate refugees’ are being displaced by changes in the Earth’s climate. Infrastructure, ecosystems, and peoples’ livelihoods have already been impacted and will continue to yield tangible evidence for the destructive effects of global climate change.


For more information, visit the University of Hawai’i Sea Level Center webpage.


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