How much will sea levels rise in the 21st Century?


Melting glaciers worldwide could result in almost 10 inches of sea level rise by the end of this century. 

The research, published in the Journal of Glaciology, indicates that the smaller glaciers could play a much larger role in sea level rise than researchers had previously thought.

The review is the most comprehensive global comparison of glacier simulations ever compiled. So far, the results have been positively chilling. When President Taft created Glacier National Park in 1910, it was home to an estimated 150 glaciers. Since then the number has decreased to fewer than 30, and most of those remaining have shrunk in area by two-thirds. He predicts that within 30 years most if not all of the park’s namesake glaciers will disappear.

Predictions for future sea levels

Future sea level rises depend on a number of factors. The amount of CO2 emitted will determine how much global warming takes place. The amount of ice that melts will vary according to the amount of global warming. The same is true of thermal expansion. Previous estimates of sea level rise have been based on a set of possible outcomes called emissions scenarios. These theoretical scenarios range from emissions which fall very quickly, to emissions that continue to rise even faster than they have already. Scientists then calculate possible outcomes for each scenario.

Other recent studies have projected comparable sea level increases. Jevrejeva 2011 for example modelled sea level rise using RPC scenarios.  ) This table shows best and worst cases (RPC3PD and RCP8.5), with two in between. The figures for each projection are listed in this table:

Table 1: Projected sea level rise (m) by 2100 for the RCP scenarios. Results presented as median, upper (95% confidence interval) and lower (5% confidence interval) limits, calculated from 2,000,000 model runs. Sea level rise is given relative the period 1980–2000. 

Another study obtained much the same results:

Figure 4: Sea level hindcasts and projections for different models calibrated with different temperature and sea level data. The error bars on the right indicate 90% confidenceintervals (5–95 percentile, using the GISS temperature dataset); for the proxy-based projection the uncertainty is as presented in Kemp et al., 2011.

“Things that normally happen in geologic time are happening during the span of a human lifetime, It’s like watching the Statue of Liberty melt.”

The IPCC projections are derived from climate models. Using both tide gauge and satellite data, we can see that sea levels are rising. Unfortunately, sea level rise is already tracking the worst-case projections, as this graph shows:

Figure 2: Sea level changeTide gauge data are indicated in red and satellite data in blue. The grey band shows the projections of the IPCC Third Assessment report .

In fact, the climate models underestimated the rate of sea level rise because the rapid melting of the ice sheets and glaciers was not incorporated in the last IPCC report.

Scientists who assess the planet’s health see indisputable evidence that Earth has been getting warmer, in some cases rapidly. Most believe that human activity, in particular the burning of fossil fuels and the resulting buildup of greenhouse gases in the atmosphere, have influenced this warming trend. In the past decade scientists have documented record-high average annual surface temperatures and have been observing other signs of change all over the planet: in the distribution of ice, and in the salinity, levels, and temperatures of the oceans. “This glacier used to be closer,” Fagre declares as we crest a steep section, his glasses fogged from exertion. He’s only half joking. A trailside sign notes that since 1901, Sperry Glacier has shrunk from more than 800 acres (320 hectares) to 300 acres (120 hectares). “That’s out of date,” Fagre says, stopping to catch his breath. “It’s now less than 250 acres (100 hectares).”

“We have more than 200 computer simulations, and they all say the same thing. Even though there are some differences, that’s really consistent.” Researchers examined the mass changes for over 200,000 glaciers worldwide, totalling an area equal to the size of Texas. The study does not include the vast ice sheets in Greenland or Antarctica, whose behaviour is different from mountain and land-based glaciers and which require unique modeling methods. The results indicate that the smaller glaciers could play a much larger role in sea level rise than researchers had previously thought. Most research has focused on ice sheets in Greenland and Antarctica, due to their size and prominence, but the effect of smaller glaciers is significant.

“Globally, there’s almost 10 inches of sea level rise by 2100 only from the smaller glaciers, whereas everybody thinks it’s only Antarctica and Greenland, But these relatively small glaciers in the world have an enormous impact,”