John’s Blog/Newsletter: SEA LEVEL RISE NOW

This popular climate change graphic was created in 2012 for my book, High Tide On Main Street: Rising Sea Level and the Coming Coastal Crisis. It has been downloaded at least hundreds of times. Recently I updated the chart for my forthcoming book. This updates the CO2 level and fixes a few minor errors in vertical scale and axis labels. If you have used the older version, I encourage you to download this update with the link shown below.

To briefly describe some of the key points that it illustrates:

• The chart spans 400,000 years. Over the long term, atmospheric carbon dioxide (CO2), global average temperature and sea level move in tight synchronization, with their peaks lining up.
• The recent ice age cycles  have been a recurring natural cycle, roughly every hundred thousand years, for several million years. The pattern follows the Milankovitch Cycles, largely determined by the changing elliptical orbit of the earth around the sun, which varies the amount of heat energy Earth receives.
• The hundred thousand year cycle is roughly twenty thousand years of warming and rising seas and eighty thousand years of cooling and falling sea level.
• For the last two and a half million years, there have been an upper and lower boundaries to global sea level, temperature and CO2. Sea level cycles up and down approximately 120 meters (390 feet), global average temperature rises and falls 5 degrees Celsius (9 Fahrenheit), and CO2 ranges between 180 – 280 parts per million(PPM).
• Now, CO2 has spiked upward, appearing as a vertical line on the chart as it passes the 400 PPM level. This level has not been reached for millions of years. The rapid increase in CO2 correlates closely with the burning of fossil fuels. In 2020 we passed a new record with CO2 at 414 PPM, 40% above the upper bound of 280 PPM that has prevailed for millions of years. (For the current level, see: https://www.esrl.noaa.gov/gmd/ccgg/trends/).
• In accordance with the natural cycle of the ice ages, we should be in the early stage of a period of eighty thousand years of cooling temperature and falling sea level with the ice sheets slowly increasing in size. In fact, the reason that sea level seemed rather stable for the last five thousand years or so, is that it was at the turning point following the upward phase and prior to the downward phase. Looking at the pattern, we can see that the current warming is an abrupt break from the natural patterns of the past.
• There is a lag time for temperature to rise with carbon dioxide and a further lag time for the ice to melt, causing sea level to rise. Yet we can already see the evidence of warming temperature and rising sea level, as the three lines proceed to maintain their long-term synchronization.
• Dividing the range of sea level change by the range of temperature change, we can easily estimate the ratio of SLR to long-term global temperature change. It works out to approximately 20 meters per degree Celsius, or about 35 feet per degree Fahrenheit. The question of how quickly the ice sheets can melt is uncertain. Ninety eight percent of potential SLR is locked up in the ice sheets of Antarctica and Greenland. Glaciologists are working very hard to better estimate the rate of glacial movement and melting, but it is very difficult to do precisely given that the ice is miles thick and twice the size of North America –– and that the future rate of warming is unpredictable due to uncertain energy policy.
• Regardless, the natural correlation of the three parameters makes clear that sea level will be significantly higher, even if we ceased all CO2 emissions immediately. It is worth noting that at the last natural high-water mark, 122,000 years ago, that sea level was approximately eight meters (twenty five feet) above present. That was part of the natural ice age cycle. As pointed out above, we are now in new territory.

To download the 400,000 year graphic of sea level, temperature, and CO2, CLICK HERE. It may be used freely without alteration, including the bottom border with the terms of Creative Commons and this website.