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Climate Change: Causes & Consequences
Donald F. Boesch
APRIL 25, 2017
Observed Warming Can Only Be Explained by Human Influences
“I would not agree that [carbon dioxide] is a primary contributor to the global warming that we see. We don’t know that yet, we need to continue the debate and the review and analysis.”
Scott PruittEPA Administrator Climate models run with only natural factors (primarily solar
intensity and volcanoes) and with both natural and human factors (primarily greenhouse gas concentrations)
How Much Warming Is Due to Human Activities?
Approximately all of it!
Fractional attribution to human causes
170 times natural factors
25% 50% 75% 100% 125% 150% 175%
110%
IPCC Fifth Assessment
No Surprise as Atmospheric Greenhouse Gases Have Increased
43.5% increase over pre-industrial concentrations
CO2 responsible for about 75% of GHG effect.Methane, nitrous oxide, CFCs most of the rest.
Concentration not seen in 4 million years
Need More Evidence?Lower Stratosphere Is Cooling
Lower stratosphere cooling
Lower troposphere & surface warming
Observed Warming Is Consistent with Climate Models
Update from Hausfather et al. 2017
1998 ENSO
2015-2016 ENSO
The Heat is Being Stored in the Ocean
Bay Waters Have Been Warming
Najjar et al. 2010. Estuarine, Coastal, Shelf Science 86:1
Ding & Elmore 2015. Remote Sensing of Environment 168: 335
Landsat satellite records: surface water warming 0.05 to 0.10° C per year, 1985-2012
Average annual temperature
(since 1985 about 0.14° F per year on average)
(almost 3° F since 1940s)
It mainly depends on how much greenhouse gases we emit.
How Much Will Earth Warm?
Global average surface temperature
Unrestrained growth in emissions
RCP 8.5
Rapid emissions reductions
RCP 2.6
7.2°F
3.6°F
www.ipcc.ch
Where we are headed
2.0°C Paris Agreement1.5°C More ambitious
We are here!
The Greater the Warming, the Greater the Risks
Maryland GGRA
Paris Agreement:
US intended reductions
Global
emissions
likely to
avoid 2°C
Pe
rce
nt
of
20
05
em
iss
ion
s
US
emissions
must be in
this range
40 by 30
25 by 20
Limiting Warming Requires Rapid Reduction of GHG Emissions
Sea-Level Has Been Rising since 19th Century
Norfolk tide gauge
Sea-level Rise in Chesapeake Bay Region
4.08 mm y-1
4.31 mm y-1
4.14 mm y-1
4.88 mm y-1
4.39 mm y-1
5.86 mm y-1
3.93 mm y-1
5.55 mm y-1
Sea-level rise1983-2013
Kopp et al. 2014. Earth’s Future
67-124 cm
44-85 cm
RCP 8.5
Sea-level Rise Projections for Baltimorewith polar ice melt & vertical land motion
Likely
RCP 2.6
Compared with 5 DoD scenarios adjusted for subsidence
Unrestrained growth in emissions
RCP 8.5
Rapid emissions reductions
RCP 2.6
Wild Card: Polar Ice Sheets
Mann & Kump 2008
Precipitation Patterns Also Affected
Sea surface temperature anomaly
Extreme Events Linked to Climate ChangeAugust 2016 Louisiana floods
• Climate change is real, primarily caused by humans and very dangerous.
• Sea-level rise will accelerate. The Bay will continue to warm, hold more water and receive more winter-spring runoff.
• We should begin to adapt and become resilient to these and other unavoidable climate changes.
• However, adaptation only will become a losing proposition by later this century.
• Without dramatic reduction in global greenhouse gas emissions by mid-century we will be confronted with conditions to which we cannot effectively adapt.
• In other words, we must manage the unavoidable while also avoiding the unmanageable.
What Science is Telling Us
