Climate Change: Science and Implications Science, Technology, Engineering, and Mathematics Seminar A DC Public Library Summer Reading Program Takoma Park Library 30 August 2014 Benjamin A. Cash George Mason University & Center for Ocean-Land-Atmosphere Studies

Issues in Global Climate Change Climate questions –Is the climate changing? How do we know? –Climate is always changing. What makes the current changes different? –How do we know humans are responsible for those changes? –How much and how fast will climate change in the future? Socioeconomic questions –What are the impacts of climate change on human socio-economic systems? –How can human activities be held accountable? –Can we take advantage of the positive effects and minimize, mitigate or adapt to the negative effects? –What local, national and international strategies can or should be employed?

Issues in Global Climate Change Socioeconomic questions –What are the impacts of climate change on human socio-economic systems? –How can human activities be held accountable? –Can we take advantage of the positive effects and minimize, mitigate or adapt to the negative effects? –What local, national and international strategies can or should be employed? Climate questions –Is the climate changing? How do we know? –Climate is always changing. What makes the current changes different? –How do we know humans are responsible for those changes? –How much and how fast will climate change in the future?

Is the climate changing? How do we know? National Climate Assessment 2014: Fig 2.1

Is the climate changing? How do we know? Multiple independent observations consistent with a warming planet National Climate Assessment 2014: Fig 2.1

Global Temperature is Increasing IPCC AR5 WG-I, °F-1.5 °F

US Temperatures Have Increased National Climate Assessment 2014: Fig 2.7 Relative to average

Frost-Free Days Have Increased NCA Fig. 2.10

Heavy Downpours Have Increased NCA Fig 2.18

The Oceans are Becoming More Acidic Ocean acidification has the potential to damage up to 50% of species of corals, mollusks and crustaceans over the 21 st century

Sea Level Has Risen NCA: Fig 16.1

Sea Level Has Risen Crisfield, Maryland, at high tide © 2013 Greg Kahn

Consistent indications of a warming climate are seen in multiple data sets

Climate is always changing. What makes this different? IPCC AR5 A Changing Climate – Temperatures are increasing – Heavy rainfall is increasing – Frost days are decreasing – Sea level is rising Doesn’t this happen all the time? – Yes. But. Not this much and not this fast.

Unprecedented Arctic Sea Ice Loss “Some 800,000 years ago - about the time early human tribes were learning to make fire – a tiny species of plankton called Neodenticula seminae went extinct in the North Atlantic. Today, that microscopic plant has become an Atlantic resident again, having drifted from the Pacific through the Arctic Ocean thanks to dramatically reduced polar ice, scientists report.” www.clamer.eu NCA Fig 2.28

Rapidly Increasing Temperatures It is likely that recent decades are warmest in past 2000 years Rate of increase is unprecedented in observational record IPCC AR5

How do we know humans are responsible for these changes? NCA Science Supplement Fig 1

Direct and Proxy measurements of greenhouse gases: Recent increases are unprecedented, at least since end of the last Ice Age (around 10,000 yr ago) From IPCC FAQ 2.1, Fig 1

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Could it be the Sun? No. Solar activity has been going down while temperature has been going up. warming.htm

How do we know humans are responsible for these changes? Climate models represent multiple physical processes and their interactions numerically Supercomputers are used to solve resulting equations Require hundreds of hours on 10’s of thousands of processors Not without flaws! Allow for “What if?” questions What if greenhouse gases had not increased? What if they continue to increase? IPCC AR5

Separating Human and Natural Influences Based on our best understanding of the climate systems at this time, recent warming trends cannot be explained by natural forcing alone NCA Fig 2.3

What Happens Next? Mostly, it depends on us. Aggressive emission reductions still lead to additional warming, but only about another 1 °F. Worst case scenario does not really bear thinking about… NCA Fig. 2.4

8” 16” 24” 32” 40” IPCC AR5 WG-I, 2013 Sea Level Will Continue to Rise

Sea Ice Disappears?

NCA Fig 16.2 Number of Hot Days Will Increase

Severity of Hottest Days Will Increase

Ecosystems will evolve NCA Fig 9.5 … probably not in a good way

Findings of the U.S. National Climate Assessment Global climate is already changing, and this is apparent across the U.S. The climate change of the past 50 years is due primarily to human activities, predominantly the burning of fossil fuels. Human-induced climate change is projected to continue and accelerate. Some extreme weather and climate events have increased in recent decades, and many of these increases are related to human activities. Climate change threatens human health. Infrastructure across the U.S. is being adversely affected. Reliability of water supplies is being reduced. Adverse impacts to crops and livestock over the next 100 years are expected, despite resilience over the next ~25 years. There are changes in biodiversity and location of species, reducing ecosystems’ resilience. Life in the oceans is changing as seawater becomes warmer and more acidic. Planning for adaptation (to address and prepare for impacts) and mitigation (to reduce emissions) is increasing, but progress with implementation is limited. In the United States, across all regions: Climate is already changing Temperature, precipitation, sea level, sea ice… U.S. infrastructure is being adversely affected Human health is threatened Water supply reliability is being reduced Crops, livestock will suffer long-term adverse impacts Ecosystems’ resilience is reduced Life in the oceans is changing

What do we do now? Resiliency and Adaptation – Climate change is happening now, and will continue into the future – Decisions made now need to take these changes into account – Decision makers need to be given accurate information on the risks, and plan accordingly Reduce, reduce, reduce – Mitigation needs to be part of any strategy. The sooner we start, the less painful it will be – Benefits beyond carbon reduction Improved air-quality Energy independence – We do not want to adapt to a worst-case scenario world