National Assessment of Potential Consequences of Climate Change Issued

Long-term observations confirm that our climate is now changing at a rapid rate. Over the 20th century, the average annual US temperature has risen by almost 1°F (0.6°C) and precipitation has increased nationally by 5 to 10%,mostly due toincreases in heavy downpours. These trends are most apparent over the past few decades. The science indicates that the warming in the 21st century will be significantly greater than in the 20th century. Scenarios examined in this Assessment, which assume no major interventions to reduce continued growth of world greenhouse gas emissions,indicate that temperatures in the US will rise by about 5-9°F (3-5°C) on average in the next 100 years,which is more than the projected global increase. This rise is very likely to be associated with more extreme precipitation and faster evaporation of water, leading to greater frequency of both very wet and very dry conditions.

The National Assessment of the Potential Consequences of Climate Variability and Change is a landmark in the major ongoing effort to understand what climate change means for the United States. Climate science is developing rapidly and scientists are increasingly able to project some changes at the regional scale, identifying regional vulnerabilities, and assessing potential regional impacts.

Science increasingly indicates that the Earth’s climate has changed in the past and continues to change, and that even greater climate change is very likely in the 21st century.

Findings that may affect North Carolina include:

• The benefits of building sea walls to prevent sea-level rise from disrupting human coastal communities will need to be weighed against the economic and ecological costs of seawall construction.

• The ecological costs could be high as seawalls prevent the inland shifting of coastal wetlands in response to sea-level rise, resulting in the loss of vital fish and bird habitat and other wetland functions,such as protecting shorelines from damage due to storm surges.
• Many ecosystems are highly vulnerable to the projected rate and magnitude of climate change. A few, such as alpine meadows in the Rocky Mountains and some barrier islands, are likely to disappear entirely in some areas. Others, such as forests of the Southeast, are likely to experience major species shifts or break up into a mosaic of grasslands, woodlands, and forests. The goods and services lost through the disappearance or fragmentation of certain ecosystems are likely to be costly or impossible to replace.
• Climate change and the resulting rise in sea level are likely to exacerbate threats to buildings, roads, powerlines, and other infrastructure in climatically sensitive places. For example, infrastructure damage is related to permafrost melting in Alaska, and to sea-level rise and storm surge in low-lying coastal areas.

This Assessment has begun a national process of research, analysis, and dialogue about the coming changes in climate, their impacts, and what Americans can do to adapt to an uncertain and continuously changing climate. This Assessment is built on a solid foundation of science conducted as part of the United States Global Change Research Program (USGCRP).

This document is the Foundation report, which provides the scientific underpinnings for the Assessment. It has been prepared in cooperation with independent regional and sector assessment teams under the leadership of the National Assessment Synthesis Team (NAST). The NAST is a committee of experts drawn from governments, universities, industry, and non-governmental organizations. It has been responsible for preparing an Overview report aimed at general audiences and for broad oversight of the Assessment along with the Federal agencies of the USGCRP.

These two national-level, peer-reviewed documents synthesize results from studies conducted by regional and sector teams, and from the broader scientific literature. This Assessment was called for by a 1990 law, and has been conducted under the authority of the USGCRP in response to a request from the President’s Science Advisor. The NAST developed the Assessment’s plan, which was then approved by the National Science and Technology Council, the cabinet level body of agencies responsible for scientific research, including global change research, in the US government.