Global warming is a reality and has been for some time. The average atmospheric temperature today is about 57° Fahrenheit and increasing. To arrest this trend, the international community hopes to achieve agreement to cap the increase at no more than 3.5° F above and ideally less.
Sea-level rise is one of the major consequences resulting from climate change. It is driven by two factors, a heated ocean and melting of landbound ice (ice already floating on the ocean does not increase sea level as it melts). At present, the single largest cause is ocean thermal expansion due to atmospheric heating.
At some point, ice melt will become the biggest contributor. A warming atmosphere and rising seas combine to increase the rate at which ice meltwater flows into the sea. About 70 percent of the world’s freshwater is on land as ice. If it all melted, sea level would rise about 215 feet. This is a very unlikely scenario, but it would not take much melting to increase sea level 10–15 feet. For example, present runoff from the largest ice field in Greenland (Jakobshavn) accounts for about 4 percent of global sea-level rise. In the West Antarctic significant ice loss will occur in the next few years. Ice shelves in that area have been deteriorating for several years, and the process is accelerating.
Scientists have consistently underestimated the accelerating rate of sea-level rise when attempting to forecast future sea levels. The current best estimate is that global sea-level increase will be in the range of 1.5–5 feet by the year 2100. However, a few experts have predicted a rise as great as 10 feet by 2050. A major unknown is how to accurately measure and forecast ice melt. At best, it’s a very uncertain science.
Sea-level rise in coastal areas is not uniform throughout the world. It tends to be regionally influenced by topography of shorelines and adjacent seafloor bathymetry. Other contributing factors can be recurring regional weather systems that modify shorelines and local land subsidence in some areas. When enough ice melts from either Greenland or Antarctica, variations in gravity will further redistribute the water.
About 44 percent of the world’s population lives within 60 miles of a coastline. This percentage is increasing despite the realities of sea-level rise. The global population’s projected increase from today’s 7 billion people to 9 billion by 2050 will further affect the fragile coastal areas.
Eight out of ten of the world’s largest cities are coastal. Studies show that by 2050, cities with the highest damage costs from rising waters include several major U.S. metropolitan areas: Miami (#2), New York (#3), New Orleans, (#4) and Boston (#8).
The price tag will be huge. In 2005 global damages from coastal flooding cost $6 billion; the estimate for 2050 is $52 billion, but it could rise to over $1 trillion if mitigation measures have not been taken by that time.
Sea-level rise could eventually make some island nations unlivable. Leaders of low-lying nations such as the Maldives, Seychelles, Kiribati, and Marshall Islands are saying that it is only a matter of time before the oceans force them to take drastic measures, including moving. If so, this would be a first in the history of mankind, as entire sovereign nations will have to relocate somewhere else.
Closer to home, in 2010 the U.S. Department of Defense began intensive risk-assessment actions to plan responses to sea-level rise. Already, encroaching seas are affecting a few of the DOD’s 704 coastal facilities worldwide.
The Navy will be especially hard hit. The fleet has few alternatives to being located in coastal areas. As a former Oceanographer of the Navy summed it up, “While our ships float, our docks do not.”
For the DOD this is a national-security issue threatening the viability of defense-infrastructure assets.
Today, there are both scientific and political controversies relating to climate change and its effects on our world. Nevertheless, change is a reality, and it is observable. Change is no longer a question of “if” but one of “when.” A major issue for the scientific community is accurately determining the rate of change and the magnitude of its effects. The earth-atmosphere-ocean system is highly interactive and extraordinarily complex. Getting good global data and developing more accurate computer modeling have been extremely difficult. But this is not an excuse for not using what data we can get to make the best possible predictions.
Dr. Walsh, a marine consultant, is a retired naval officer and oceanographer. During his naval career he served at sea in submarines and ashore in ocean-related research-and-development assignments.