Ice sheets and glaciers are the largest contributors to sea level rise, with a potential to drastically raise the sea level globally. Summer sea ice is decreasing rapidly and may vanish entirely within the next decades, and multi-year ice (sea ice that remains for more than one year without melting) is in decline. These changes in the world’s polar ice, despite its remote location, have global economic and health implications as climate changes.
NISAR will determine how the behavior and evolution of ice masses will contribute to sea level rise. NISAR will measure changes in sea ice, snow extent, permafrost, and surface melting. Ice sheets, sea ice and glaciers, which are all key indicators of climate effects, are undergoing dramatic changes. Rising sea level from melting ice sheets poses hazards to coastal areas from storm surges and erosion. Diminishing sea ice is changing shipping lanes and the availability of resources. Measurements taken now will be used to predict future changes.
Assessing Society's Exposure to Diminishing Ice
For more than 100 years, scientists have considered diminishing glaciers and sea ice to be an early indicator of global warming. Ice sheets and glaciers are already melting fast enough to be the largest contributors to sea level rise, with a potential to raise sea levels substantially in the coming century. Satellite observations collected over the past three decades show that summer sea ice cover is decreasing drastically and may vanish entirely within decades. This loss will have a profound effect on life, climate and commercial activities in the Arctic, while the loss of land ice will impact an important source of water for millions of people. Collectively, these effects mean that ice loss — even in remote regions — has global economic and health implications as climate changes.
Improving Sea Level Projections
Flow rates and melt rates of coastal glaciers in many parts of Greenland and Antarctica have increased significantly as ice is lost to the sea, more than doubling in some cases. These changes have caused the glaciers to thin significantly. These coastal glaciers often act as a buttress holding back interior ice. When they are lost, the lack of buttressing makes the ice sheets unstable and is likely to lead to a more rapid rise in sea level.
Rising seas could displace millions of people and adaptation will be costly, but predicting the rate of future sea level changes is difficult at present. Recent observations provide only isolated snapshots of ice sheet velocity and changes, and current satellite missions map large-scale ice sheet changes but lack the resolution to monitor many fast-moving, rapidly thinning glaciers. NISAR will provide systematic measurements that record both short-term variations and long-term trends. NISAR will also provide a time history of ice sheet and glacier behavior. It will provide precise measurement of the changing position of ice sheet grounding lines. These new, high-resolution data will improve projections of sea level rise from melting glaciers and ice sheets. Accurate sea level projection will improve planning of sea walls, dikes and other mitigation strategies.
Tracking Sea Ice and Monitoring Permafrost
Arctic sea ice has thinned and its summer extent has reduced by as much 50% over the last several decades. By contrast, sea ice cover in the Southern Ocean may be increasing slightly in extent, but there is very little information regarding its surface and thickness. The thinning and retreating Arctic ice cover is changing the economy of local communities by causing a shift in the patterns of marine wildlife and an increase in winds and waves, as well as stimulating interest in petroleum development and shipping. NISAR will provide key data necessary to make informed environmental and economic decisions.
NISAR will provide the most complete measurements of rapidly changing sea ice in both polar regions. Understanding the causes and mechanisms of ice loss requires knowledge of ice thickness, sea ice types and sea ice dynamics. Melting permafrost releases methane to the atmosphere, erodes soil and impacts surface water distribution and the stability of infrastructure. NISAR will measure heave and thaw in the near-surface active layer of permafrost.
Mountain Glaciers and Ice Caps: Indicators of Climate Change
Glaciers outside of the ice sheets are among the most important indicators of climate change, contribute to rising oceans, and augment fresh water supplies during critically dry conditions. Currently, glaciers account for approximately one third of present-day rates of sea level rise. In regions such as High Mountain Asia, that includes the Himalayan range, glaciers and snow augment water supplies of highly populous regions. Systematic observations of snow and ice in these regions will improve our understanding of underlying processes acting on them and how they will respond as the climate changes. NISAR radar, with its greater ability to resolve snow mass, large swath, and frequently repeated observations, will enable the study of snow and glaciers at much improved scales.