Agriculture Reference
In-Depth Information
warmer than any decade since 1850 (IPCC 2013). In the Midwest, the largest tem-
perature increases have occurred at night and in the winter (Pryor et al. 2014),
and the length of the frost-free season has increased by 9 to 10 days across the
NCR, leading to a longer growing season (Walsh et al. 2014). Since 1991, pre-
cipitation has increased across most of the NCR by 8 to 9%, as has the frequency
of heavy downpours, especially in the Midwest and northern portion of the Great
Plains region (Walsh et al. 2014). Heat waves have also increased, with three times
the long-term average number of intense heat waves in 2011 and 2012 across the
United States (Walsh et al. 2014).
Temperature trends in Michigan reflect global patterns with a cooling period
from 1930 through 1980 followed by a warming trend beginning in the early 1980s
(Andresen 2012). The warming has been concentrated in the winter months and
mostly reflected in higher minimum temperatures. Mean precipitation has generally
increased since the late 1930s—but with dry conditions in the late 1950s and early
1960s—as has the number of days with measureable precipitation, which is associ-
ated with more cloudiness (Andresen 2012). The decreasing amount and duration
of ice cover on the Great Lakes have significant implications for Michigan's cli-
mate as the Great Lakes tend to moderate the local climate downwind of the lakes
(Andresen 2012).
Climate Projections
For the next two decades, warming of 0.3 to 0.7°C in global mean surface air
temperature is projected under a range of greenhouse gas scenarios, and even if
greenhouse gas emissions are stopped, changes in the climate will continue for
many centuries (IPCC 2013). By the end of the twenty-first century, projections
of warming range from 0.3°C to 4.8°C depending on greenhouse gas emissions
and other drivers, with projections showing a 1.5°C increase as likely under most
emission scenarios (IPCC 2013). The highest rates of warming are expected to
be over land, with more warm days and nights and fewer cold days and nights.
Increases in the frequency of heat waves and heavy precipitation events are likely,
with the contrast in precipitation between wet and dry regions of the globe increas-
ing (IPCC 2013).
Climate change projections for specific regions are generally much more uncer-
tain than global projections, and regionally focused studies are not yet available for
every location (NRC 2010b). However, models consistently agree with projections
of warmer annual temperatures for the NCR for both summer and winter months
(IPCC 2013, Walsh et al. 2014), and the trend of longer frost-free and growing
seasons is projected to continue for the region (Walsh et al. 2014). There is greater
uncertainty in precipitation projections. For the northern half of North America,
projections show increases in mean annual precipitation over winter and spring
months, but models do not agree on summer or fall precipitation changes (IPCC
2013, Walsh et al. 2014), making it difficult to predict regional effects on agricul-
ture. There is, however, high certainty that heavy precipitation events will increase
in frequency and intensity, and the number of consecutive dry days is projected to
increase (Walsh et al. 2014).
