The main greenhouse gases are methane, nitrous oxide, fluorocarbons, water vapor, and carbon dioxide (CO2) and optimum amounts are vital for life on Earth. Carbon dioxide is not the most absorbent gas but it is very abundant and can remain in the atmosphere for a century or longer. World-wide, CO2 levels have varied greatly over time. During past glacial periods of cold climates, the amount of CO2 in the atmosphere was about 180 parts per million (ppm). During interglacial warm periods, CO2 was about 280 ppm. Today the concentration is 390 ppm, a 30% rise since the Industrial Revolution in the mid-1800s and higher than any time in Earth’s history for the past 15 million years.
- · Increase in air and ocean surface temperature
- · Increase in rainfall intensity; more variability in rain and drought patterns
- · Increase in the rate of sea level rise
- · Increase in coastal erosion and loss of beaches, dunes, and wetlands
- · Increased ocean acidification
- A dynamic and changing global climate has long been part of a natural Earth cycle; however, human activities, particularly carbon emissions into the air since the mid-1800s have increased global warming causing a variety of well documented and pervasive environmental change. These changes are increasing risk of hardship and hazards to humans, especially along coasts and low-lying regions.
- Sea level rise, in concert with storms and geophysical conditions, is a main driver of coastal erosion and shoreline retreat. Sea level has risen one foot over the past century; rates have increased 50% since 1990, and global average sea level is expected to rise as much as 3 to 5 feet by the end of this century. Higher rates of warming and ice sheet melting and changes in wind and ocean circulation patterns may further increase the projected rise in sea level.
- The probability of continued global warming and sea level rise is high and planning for long-term strategic adaptation to these changes is needed now. Plans should be based on credible science, engineering, and economics and consider all costs and benefits to strive toward sustainable coasts, coasts that maintain natural processes but also are able to accommodate human uses.