Download Key Questions about Climate Change2015

Key Questions about Climate Change
Is the lower atmosphere becoming warmer?
1)
2)
3)
4)
Global temperature rose at an average rate of about
0.13°C per decade for the past 50 years. 2014, 2015,
and 2016 are the warmest since measurements began
in 1850s. http://www.climate.gov/
Globally representative mountain glaciers with the
longest, most reliable records lost 57 feet of thickness
1980 – 2014.
Global average sea level rise has accelerated from 1.7
mm/year throughout most of the twentieth century to
3.2 mm/year since 1993. (thermal expansion & melting)
Sub surface ocean temperatures (upper 75m) have
warmed 0.09 to 0.13°C per decade since 1971 (when most
thorough measurements began)
Source: http://www.climate.gov/
2. Have human activities caused global warming?
Some background:
• Showing human causation requires both demonstrating
1) that human emissions can account for the observed
warming trends, and 2) showing that other potential
explanations cannot.
• The past earth climate has shown significant temperature
variability long before human societies were capable of
causing it.
Natural Causes of Temperature Variability:
1.
a)
b)
c)
2.
3.
Earth-sun orbital variations –
Average earth-sun distance varies over ~100,000 yr. cycle
Seasonal timing of perihelion varies in ~26,000 yr. cycle (currently in
cold phase for N. Hemisphere: July 4)
Axial tilt varies from ~22° to 25° over a ~40,000 yr. cycle (currently in
decreasing phase, 23.44 degrees)
There is strong scientific consensus that these cycles are associated
with the cycling between ice ages and warm interglacial periods over
the past few hundred thousand years. These changes are slow and
thus unlikely to have caused the rapid warming of the last 100 yrs.
Tectonic activity affects latitudinal locations of continents and
geochemical processes that can affect total snow cover and
atmospheric chemistry. Such changes are too slow (millions of
years) to have caused the rapid warming of past 100 yrs.
Volcanic eruptions put dust, droplets and ash into the atmosphere,
blocking sunlight and cooling temperatures. No trends in recorded
eruption history suggest sustained reductions in past few centuries.
Natural Causes (con’t)
4.
5.
6.
Solar output has showed little or no upward trend since
1978, when satellites began measurement, only
periodic variation of less than 0.1% in 11 yr. cycles.
Earlier records of sunspot activity (related to solar
output) suggest an increase in solar radiation dating
back ~two centuries, but not recently.
Earth system internal variability, such as the episodic El
Nino-Southern Oscillation (warming), can have large
effects on temperatures. However, between 1000 and
1800, the overall proxy record shows nothing similar to
the rate of warming seen since the late 19th century.
Therefore, there is no compelling evidence that forcing
mechanisms (#1-4), or internal variability (#5), or a
combination thereof can account for the rate of warming
of the past century.
If natural causes and variability do not appear to
have caused most of recent warming, are human
activities sufficient to have caused it?
Human activities have increased the concentrations of CO2
(30%) and other greenhouse gasses over past few
centuries. Basic physics provide support for the
warming role of greenhouse gasses, as do climate
models that are based on physics, and empirical
observations.
The Intergovernmental Panel on Climate Change has
concluded that “…most of the observed warming over
(the years 1950-2012) is likely to have been due to the
increase in greenhouse gas concentrations.”
Remember the process in which greenhouse
gasses help warm the atmosphere…
• Some of the shortwave radiation from the sun
penetrates the atmosphere, and is absorbed by
the earth’s surface, which warms up. Then, the
earth emits longwave radiation, some of which is
absorbed by the greenhouse gasses in the
troposphere. Thus, solar radiation warms the
earth’s surface, and then earth radiation warms
the troposphere. (Note: surface air is also
warmed through turbulent heat transfer from the
heated earth.)
3. What future changes in global climate are expected?
• Future temperatures are likely to be driven mostly by
future concentrations of greenhouse gasses, which will
depend on future emissions, which will be driven by
•
•
•
•
•
population increase
world economic growth
technological trends
policies
historical events such as major wars, political transitions, or
emergence of epidemic diseases
• Global warming is likely to continue as greenhouse gas
concentrations rise.
• The higher N. latitudes are expected to continue to show
the greatest temperature changes
• Is the intensity of hurricanes and other storms likely to
increase?
4. What are likely impacts of global warming ?
•
Island & coastal populations, and low income countries will have the most
difficulty mitigating negative impacts
• Food security risks are greatest for those who are poor, isolated, landless,
and/or living near sea level (example Bangladesh
https://www.youtube.com/watch?v=NdZhD8zhiS0)
• 280 million people depending on coral reef environments for a significant
part of their food intake will need to migrate or import more food
• High latitude regions may see increased grain production (mostly wealthy
countries including Canada, Scandinavian nations, Russia)
• Expansion of the latitudes and altitudes of diseases, including malaria,
dengue fever, yellow fever (all mosquito vectored).
• Regions relying on snowmelt waters will have to make changes.
• Second and third order impacts are difficult to predict, but can be potentially
devastating. Example: Western Pine Beetle killing millions of forest acres
http://www.wou.edu/~mcgladm/Geography%20313%20Pacific%20Northwest/fo
r%20exam%201%20physical%20landscape/optional/optional%20bark%20b
eetle%20outbreaks%20related%20to%20warming.pdf
http://www.nytimes.com/2008/11/18/science/18trees.html?em
Warmer temperatures cause trees to be more drought stressed, and thus
are less able to secrete enough pitch to immobilize larvae. Extreme winter
cold used to kill many overwintering beetles, but winters of past 30 yrs. are
not so cold. Longer warm seasons allow more reproduction.