Why? Because our entire society has been built around the climate of the 20th century (and to some degree the climate of the last couple thousand years). Where we grow crops, how we store and distribute water, where we have built cities, and how we have built infrastructure for resiliency against weather and climate variability are a function of that 20th century climate (and to some degree the climate of the preceding centuries).
Here are some examples. Water is the agent that delivers most climate impacts and even if there are a few winners with climate change, everyone loses with sea level rise. Most of the worlds largest urban areas sit in coastal areas. In the United States, more than 50% of the population is near coasts and approximately 3.7 million people living within 1 m elevation of mean high tide (TIDEL).
|Source: Strauss et al. (2012)|
How about National Security? The Center for Naval Analyses Military Advisory Board, comprised of retired high-level officers and generals fro the armed forces, issued a report this week entitled National Security and the Accelerating Risks of Climate Change. Again we see here that a shift in the climate is a societal stressor:
"The projected impacts of climate change will be more than threat multipliers; they will serve as catalysts for instability and conflict."One interesting case study discussed in the report is the impact of sea level rise on the military infrastructure in the Hampton Roads area of Virginia (p. 25), which includes 29 military sites and serves as home for 20% of the U.S. military fleet. This is a low lying area in which significant adaptation efforts will be needed.
"As the world's population and living standards continue to grow, the projected climate impacts on the nexus of water, food, and energy security become more profound. Fresh water, food, and energy are inextricably linked, and the choices made over how these finite resources will be produced, distributed, and used will have increasing security implications."
"Projected climate change impacts inside the borders of the United States will challenge key elements of our National Power and encumber our homeland security. Of particular concern are climate impacts to our military, infrastructure, economic, and social support systems."