Human response to climate change - The Global Climate System: Patterns, Processes, and Teleconnections - page 283

a5.08C increase and no precipitation change was estimated to be (for 2060)
a national annual loss of $19.9 billion (1998 dollars). Mendelsohn and
Smith noted that these various predicted economic impacts would be about
0.1 percent of the GDP expected by 2060, and they further note their values
are about an order of magnitude less than those of the IPCC (1996).
A recent national assessment of climate change involved an in-depth
investigation of the consequences of climate change in the United States
with impacts assessed based on conditions predicted by two global climate
models: the Hadley model and the Canadian climate model (NAST 2001 ).
Thousands of potential effects were identified (for example, less water, more
heat waves, and altered crop seasons, etc.), but few of these impacts were
translated into financial outcomes. The agricultural sector assessment found
that the projected conditions increased yields of many crops, including corn,
wheat, and soybeans. The agricultural impact assessment did quantify the
economic outcomes showing that the Canadian model conditions, given
various adoption strategies, ranged from losses of $0.5 billion (2000 dollars)
annually to gains of $3.5 billion, whereas the Hadley climate model conditions
resulted in agricultural benefits ranging between $6 billion and $12 billion
(2000 dollars) annually. In comparison, an agricultural assessment of the
1950-2000 period found an average annual benefit of $1.9 billion (1997
dollars) with a one-year peak of $4.8 billion (Changnon and Hewings 2001 ).
When losses occurred, the average annual loss was $2.6 billion (1997 dollars).
The concluding chapter of the national assessment states, ''For the nation as a
whole, direct economic impacts are likely to be modest'' (NAST 2001).
The above listed economic estimates of losses and gains from a future
changed climate must be considered quite speculative. Recent papers by
economists, all familiar with the climate change issue, revealed the difficulty
of estimating, even crudely, the future economic impacts of global warming
and the costs of various approaches for mitigating climate change. As Yohe
( 2003 ) stated, ''How could we estimate the distribution of costs and benefits
(of mitigating climate change) across the wide range of unknown and unpre-
dictable economic and climate futures?''
Furthermore, estimating national impacts based on shifts in the nation's
climate does not take into consideration external impacts. Climate changes in
other parts of the world, particularly in developing nations, may create financial
impacts that greatly influence the United States' economy. All of this adds to
the uncertainty in estimated future economic impacts in the United States.

8.5 Conclusions
The discussion in the chapter establishes that adaptation to climate is an essential
component in human life, whether the society is based on subsistence