Download 1) Indications of changes in global temperatures

The Future of the Earth’s Habitable Zone
Goals
Review the concept of a habitable zone
• Introduce the concept of “continuously habitable zone”
• How will the Earth’s habitability end?
• Global climate change
•
1
The habitable zone (review)
The range of distances around a star, at which a planet could
potentially have conditions that would allow for abundant amounts of
liquid water on the planet’s surface.
Venus: Earth’s twin
M=0.815×MEarth
R=0.949×REarth
D=0.723 a.u.
Atmosphere: 90 atm
Composition: 96% CO2
Temperature: 470ºC; 880ºF (Not 35ºC; 95ºF)
What would happen to the Earth, at Venus’ position in the solar system?
Temperature rise  increased oceanic evaporation;
Increased atmospheric H2O  increased greenhouse effect;
((Repeat, repeat, repeat))
The Earth becomes a new Venus.
2
Our Sun’s habitable zone (Review)
Inner boundary
– Determined by a runaway greenhouse effect;
– Somewhere between 0.7 a.u. (Venus) and 1 a.u. (Earth).
– Standard models suggest the boundary ~ 0.84 a.u.
– “Moist greenhouse effect” models suggest ~ 0.95 a.u.
Outer boundary
– Determined by the greenhouse effect’s ability to keep water in
liquid state, despite being so far from the Sun;
– Somewhere between 1.0 a.u. (Earth) and 1.5 a.u. (Mars).
If Mars had a stronger greenhouse effect (perhaps as in the past), it
would be within a habitable zone limit ~ 1.7 a.u.
But, some models suggest CO2 snow would rob a planet of its CO2
atmosphere at distances exceeding ~ 1.4 a.u.
Summary: our Sun’s habitable zone is
0.95 —1.4 a.u. -or0.84 — 1.7 a.u.
3
Mars and the habitable zone
Just because a planet is habitable one day, it will not necessarily be
habitable tomorrow!
Consider Mars—the evidence is extremely strong that it has known
liquid water on its surface:
Weathered features as viewed from space;
– Carbonate deposits on the Martian meteorite suggesting pulses of
water flows;
– Features such as hematite blueberries as detected by rovers.
–
The hematite blueberries suggest Mars was continuously habitable over
long periods of time.
Mars is no longer habitable because it cooled, solidified, lost its
magnetic field, and was solar-stripped of its atmosphere.
4
Solar brightening: our evolving sun
The Sun is not the unchanging energy source you may think it is.
The Sun supports itself against inexorable gravity by energyreleasing nuclear reactions in its core:
1H
+ 1H + 1H + 1H  4He + ENERGY
Over time, the number of particles in the Sun’s core
decreases….
…With fewer particles in the core, they have a harder time
fighting gravity…
…The result is that the core compresses; in the process, it heats
up…
…and the hotter, compressed core burns more furiously.
The Sun is about 30% brighter now than it was when it formed
Furthermore, it will continue to brighten into the future!
5
Continuously habitable zone
As the Sun brightens over time, its habitable zone slowly changes—
both edges of the habitable zone are moving away from the Sun.
The continuously habitable zone is the range of distances from the
Sun that have been continuously habitable since the Solar System’s
creation.
Estimates of the continuously habitable zone depend upon our
assumptions about habitability, and the solar brightening.
What about us—what about the future?
As the Sun gets hotter, the habitable zone of the solar system will
move outwards, away from the sun.
We will be driven from the Earth. Where will we go?
6
The ultimate end of our habitable zone
Event
Solar brightening
Timescale
0.5-3 BY
Escape to…
Mars, interplanetary space
Red giant phase (1000Lsun)
(Earth is 700ºC, 1300ºF)
5 BY
Interplanetary
space
Planetary nebula phase
(Earth probably vaporized)
5+ BY
Other stars
Milky Way Galaxy exhausted
(star formation ends)
50 BY
K, M stars
K, M stars die
100 BY
??
??
---
Black holes evaporate;
Protons decay;
Universe a sea of dilute photons
7
Global Climate Change
– Evidence for “global warming”
– Connection with greenhouse gases
– Is the greenhouse gas emission anthropogenic?
– Potential consequences
– Uncertainties
Frequent complaint
“We can’t predict the weather for this week—why are you saying
we can predict the weather for years to come?”
Weather is not climate. Climate is saying, “Florida is hotter than
New York; Arizona is more arid than Seattle” This, we can predict.
8
Evidence for global climate change
1. Data must be long-baseline;
2. Data must be obtained consistently;
3. Data should be insensitive to short duration effects.
Statements that are not scientifically significant include:
– Wow, this year is really hot!
– Wow, this year is really rainy!
– Wow, the last two years we’ve had bad hurricanes!
Longer baselines are needed to justify such statements.
Huge ice deposits (such as glaciers or arctic/antarctic ice fields) help monitor
overall global temperatures because…
– They have large thermal inertias, making them insensitive to minor yearly
variations.
– They are made of water, which is (on Earth) near the cusp of being liquid
vs. solid.
9
Evidence for global climate change
Time to take a tour! Start by leaving Sewell
Destination #1
Pederson Glacier; Kenai Fjords National Park, Alaska.
From 1920 to the current, we have seen the recession of
glaciers and the evaporation of the lagoon at the base of the
glacier.
Destination #2
Muir Glacier; Glacier Bay National Park & Preserve, Alaska.
The glacier has retreated by 20 km since 1941, this involved
the melting of glacier ice 65 m thick.
10
Evidence for global climate change
Destination #3
Greenland.
The Greenland ice sheet is melting faster than it grows, and is
therefore shrinking.
Destination #4
Larsen B Ice shelf; Antarctica.
The Larsen A ice shelf broke up in 1996,
the Larsen B ice shelf broke up in 2002 (over 3 weeks);
Larsen B had an area of Rhode Island.
Its speed of break up has astonished and thrilled scientists.
And on and on and on…a long parade of additional examples
is found planetwide.
11
Connection with greenhouse gases
We know from studying Venus, Earth, and Mars, that the greenhouse effect is active
and important.
Without the greenhouse effect, the Earth would be -18ºC (0ºF), but with it the Earth is
about 14ºC (57ºF).
We know the gases that contribute to the greenhouse effect on the Earth1:
H2O: 36-72%
CO2: 9-26%
CH4: 4-9%
O3: 3-7%
Other gases include N2O and CFCs.
H2O vapor is rapidly regulated by the planet’s climate.
CO2 is slowly regulated by the long CO2 cycle.
12
Connection with greenhouse gases
Global climate change is an issue involving four factors. Do we see…
1) Changes in global
temperatures?
3) Correlations between global
temperatures and greenhouse
gas concentrations?
4) Contributions to the
greenhouse gas concentrations
by our activities?
2) Changes in concentrations
of greenhouse gases?
Remember that the greenhouse effect is enormous (32ºC, 57ºF) and unquestioned.
Global climate change asks whether the greenhouse effect is changing. The change
being discussed is tiny compared to the massive greenhouse effect.
13
Global temperatures and greenhouse gases
1) Indications of changes in global temperatures
150 years worth of land-water temperature measurements were analyzed
by NASA scientists.2 Note the observed increase in temperature since
1920.
2000 years of temperatures, inferred from ice cores, tree rings, pollen,
sediment measures, etc., record climate events such as the medieval warm
period and little ice age.3 These measures also indicate that the recent
temperature increase is greater than in any other measured time.
2) Indications of changes in greenhouse gas abundances
In Hawai’i, on the northern slope of Mauna Loa at 3400 m (11,000 feet),
probes are recording atmospheric CO2 measurements.4 This overall rise is
called the Keeling curve, and is observed at other research stations, too.
The tiny periodic changes are due to CO2 uptake by plants (northern
forests dominate this, so the CO2 drops during the northern hemisphere
summer).
14
Global temperatures and greenhouse gases
3) Indications of a correlation between temperatures and
greenhouse gases
Blue data—temperatures inferred from deuterium abundances at the
Antarctica research site called Dome C.
Green data—Temperatures inferred from deuterium abundances at Lake
Vostok.
Red data—Global ice volume (hence, global temperatures) inferred from
18O isotopes, related to fractionation from planktonic sediments.
Note the agreement of the three temperature measures with each other.
CO2 data at bottom—ice core data from Lake Vostok (blue), Dome C core
(green), Law Dome (red), Siple Dome (cyan); atmospheric Mauna Loa
(black).
Note the excellent correlation between temperature and CO2
concentrations.4, 5
15
Global temperatures and greenhouse gases
4) Indications of contributions to the abundances of
greenhouse gases by humans
Note that the global levels of carbon emission have risen steeply, since
around 1920.5
Recall 1920 is the approximate date at which we saw global
temperatures rise in the 150-year graphic.
A regional breakdown of CO2 indicates that we are a chief culprit.6
Expect to see China’s contribution become increasingly important.
Note that it is easy to complain about the “Amazon rainforests being
burned” when it is someone else’s error!
16
Potential future consequences
Polar regions
– The arctic should see 3-8ºC increase this century. Seasonal
ice sheets will diminish.
– Expect a population collapse in polar bears and other arctic
species. (The polar bear is a keystone species.)
Albemarle Peninsula
– Globally, the sea level is rising 0.3-0.5 cm per year. The
shoreline of North Carolina is changing: freshwater
environments are becoming saltwater marsh.
– Thousands of acres have been lost, 50 cm of sea level rise
will result in 750,000 acres being lost.
Florida keys
– Sea warming contributes to coral bleaching. Reefs around
the world are dying.
– Expect extraordinary losses of marine biodiversity.
17
Other potential future consequences
Changing ranges of diseases
This is possibly a shell game.
More severe storms
The Atlantic storm intensity has doubled during the last 30 years.
More extreme climate variations
Californian impacts
Increased winter precipitation but decreased snowpack;
Increased summer temperatures;
Dryer summers (without snowmelt waters);
Increased wildfires.
18
Sources cited
1Kiehl,
J. T.; Kevin E. Trenberth (February 1997). “Earth’s Annual Global Mean Energy Budget”.
Bulletin of the American Meteorological Society 78 (2): 197-208.
J., Mki. Sato, R. Ruedy, K. Lo, D.W. Lea, and M. Medina-Elizade (2006). “Global
temperature change”. Proc. Natl. Acad. Sci. 103: 14288-14293.
2Hansen,
3Rhode,
R.A. (2011). “Global Warming Art”.
http://www.globalwarmingart.com/wiki/Temperature_Gallery, accessed 2/2011.
4Rhode,
R.A. (2011). “Global Warming Art”.
http://www.globalwarmingart.com/wiki/Carbon_Dioxide_Gallery, accessed 2/2011.
5Rhode,
R.A. (2009). Data from “Global Warming Art”.
http://www.globalwarmingart.com/wiki/List_of_temperature_related_images, accessed 2/2011,
modified by Rice, B.A.
6Marland,
G., T.A. Boden, and R. J. Andres (2003). “Global, Regional, and National CO2
Emissions" in Trends: A Compendium of Data on Global Change. Oak Ridge, Tenn., U.S.A.:
Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory, U.S. Department
of Energy.”
19