Download Methane, Plants and Climate Change

Methane, Plants and Climate
Change
Scientific American
Current Issues in Biology
Volume 5
Lectures by Greg Podgorski, Utah State University
Copyright © 2009 Pearson Education, Inc. publishing as Benjamin Cummings
Methane, Plants and Climate Change
Concept Review
• What do you do when you find something that
contradicts the textbooks?
•Frank Keppler and Thomas Röckmann faced this
question when they found a new source of methane –
living plants.
• Their answer?
• Repeat your experiments to be sure of your results,
then tell the world through a publication reviewed by
other scientists.
Copyright © 2009 Pearson Education, Inc. publishing as Benjamin Cummings
Methane, Plants and Climate Change
Concept Review
• Methane (CH4) is best known as “natural gas.”
• Methane is an important greenhouse gas.
• Pound-for-pound, methane is 23 times more
effective than carbon dioxide in trapping heat.
• Human activities have tripled the levels of
atmospheric methane over the past 150 years.
• Roughly 600 million metric tons of methane are
produced annually.
•Knowing all sources of methane is essential if its
levels are to be controlled.
Copyright © 2009 Pearson Education, Inc. publishing as Benjamin Cummings
Methane, Plants and Climate Change
Concept Review
• The finding that plants produce
methane flew in the face of
conventional wisdom.
• By 2001, the
Intergovernmental Panel on
Climate Change (IPCC)
believed all major sources of methane had been
identified.
• Plants were not on the list.
Copyright © 2009 Pearson Education, Inc. publishing as Benjamin Cummings
Methane, Plants and Climate Change
Concept Review
• Prior to Keppler and Röckmann’s discovery, the major
known sources of methane were:
• Anaerobic bacteria (including those that live in the
digestive systems of cows and other ruminants)
• Forest and savannah fires
• Burning of fossil fuels
• But based on these sources, fluctuations in methane
levels before humans started burning fossil fuel (during
the Industrial Revolution) could not be explained.
Copyright © 2009 Pearson Education, Inc. publishing as Benjamin Cummings
Methane, Plants and Climate Change
Concept Review
• The discovery that living
plants produce methane was
accidental.
• Keppler and Röckmann were
interested in chloromethane, a
gas that destroys ozone.
• They knew that decaying plant material produced
chloromethane, and wondered if it also made methane.
• They found that tiny amounts of methane were
produced by dried plant material.
Copyright © 2009 Pearson Education, Inc. publishing as Benjamin Cummings
Methane, Plants and Climate Change
Concept Review
• What about living plants?
• They found that living plants produced 10 to 100
times more methane than dried plant material.
• The amount of methane produced by each plant is
small, but the cumulative amount is huge.
• Keppler and Röckmann estimated that plants produce
60 – 240 million metric tons of methane annually.
Copyright © 2009 Pearson Education, Inc. publishing as Benjamin Cummings
Methane, Plants and Climate Change
Concept Review
• According to these figures, plants could be responsible
for 10% to 40% of global methane emissions.
• Keppler and Röckmann knew that current views about
methane production would make it difficult for many
scientists to accept these figures.
• Strengthening their case, two independent lines of
evidence were discovered that supported links between
plants, methane, and climate change.
Copyright © 2009 Pearson Education, Inc. publishing as Benjamin Cummings
Methane, Plants and Climate Change
Concept Review
•Satellite observations showed huge clouds of methane
over tropical forests that couldn’t be explained by
existing models.
• A reanalysis of
previous data showed
massive releases of
methane from tropical
savannah, which is
explained by plant methane production.
• Even so, many scientists remain skeptical of the
magnitude of methane production by plants and are
repeating Keppler and Röckmann’s studies.
Copyright © 2009 Pearson Education, Inc. publishing as Benjamin Cummings
Methane, Plants and Climate Change
Concept Review
• Understanding that plants produce methane explains
previous puzzling observations.
• Methane levels were known to vary in step with the
Earth’s temperatures.
Copyright © 2009 Pearson Education, Inc. publishing as Benjamin Cummings
Methane, Plants and Climate Change
Concept Review
• The plant-methane link also means that global
warming will drive further increases in temperature.
Warmer Earth
More plants
More methane
Copyright © 2009 Pearson Education, Inc. publishing as Benjamin Cummings
Methane, Plants and Climate Change
Concept Review
• The media ran headlines like “Global Warming –
Blame the Forests.”
• Plants have been emitting methane for hundreds of
millions of years.
• They have not caused the sharp increase in methane
output seen since the Industrial Revolution.
Copyright © 2009 Pearson Education, Inc. publishing as Benjamin Cummings
Methane, Plants and Climate Change
Concept Review
• Plants are an essential source of the oxygen on
which life as we know it depends.
• The major cause of global warming is not plants – it’s
the burning of fossil fuels.
Copyright © 2009 Pearson Education, Inc. publishing as Benjamin Cummings
Methane, Plants and Climate Change
Concept Review
• Plant production of methane raises a serious concern.
• Which is greater – the benefit of carbon sequestration
from planting forests, or the harm caused by the
methane those forests give off?
• Calculations show that the benefit of planting more
trees is greater.
Copyright © 2009 Pearson Education, Inc. publishing as Benjamin Cummings
Methane, Plants and Climate Change
Testing Your Comprehension
Methane is also known as:
a) chlorofluorocarbon.
b) chloromethane.
c) natural gas.
d) liquefied butane.
Copyright © 2009 Pearson Education, Inc. publishing as Benjamin Cummings
Methane, Plants and Climate Change
Testing Your Comprehension
Methane is also known as:
c) natural gas
Copyright © 2009 Pearson Education, Inc. publishing as Benjamin Cummings
Methane, Plants and Climate Change
Testing Your Comprehension
Methane is:
a) becoming toxic to plants at its current levels.
b) more effective than carbon dioxide at trapping heat.
c) a major contributor to acid rain.
d) taken up by plants for use in photosynthesis.
Copyright © 2009 Pearson Education, Inc. publishing as Benjamin Cummings
Methane, Plants and Climate Change
Testing Your Comprehension
Methane is:
b) more effective than carbon dioxide at trapping heat.
Copyright © 2009 Pearson Education, Inc. publishing as Benjamin Cummings
Methane, Plants and Climate Change
Testing Your Comprehension
The discovery that living plants produce methane
happened by accident when scientists were studying:
a) the sources of an ozone-destroying gas.
b) how plants produce oxygen during photosynthesis.
c) how plants absorb carbon dioxide.
d) the ecology of savannah ecosystems.
Copyright © 2009 Pearson Education, Inc. publishing as Benjamin Cummings
Methane, Plants and Climate Change
Testing Your Comprehension
The discovery that living plants produce methane
happened by accident when scientists were studying:
a) the sources of an ozone-destroying gas.
Copyright © 2009 Pearson Education, Inc. publishing as Benjamin Cummings
Methane, Plants and Climate Change
Testing Your Comprehension
Knowing that plants produce methane solves the longstanding mystery of:
a) the winter ozone hole over the Antarctic.
b) global warming.
c) why plant biomass increased during interglacial
periods.
d) the coupling between atmospheric methane and
changes in Earth’s temperature.
Copyright © 2009 Pearson Education, Inc. publishing as Benjamin Cummings
Methane, Plants and Climate Change
Testing Your Comprehension
Knowing that plants produce methane solves the longstanding mystery of:
d) the coupling between atmospheric methane and
changes in Earth’s temperature.
Copyright © 2009 Pearson Education, Inc. publishing as Benjamin Cummings
Methane, Plants and Climate Change
Testing Your Comprehension
Warmer Earth
More plants
More methane
If not interrupted, the cycle above leads to:
a) a spread of plants across every land area.
b) the destruction of all large life forms.
c) ever-increasing global temperatures.
d) an equilibrium between global temperature, plant life,
and methane levels.
Copyright © 2009 Pearson Education, Inc. publishing as Benjamin Cummings
Methane, Plants and Climate Change
Testing Your Comprehension
Warmer Earth
More plants
More methane
If not interrupted, the cycle above leads to:
c) ever-increasing global temperatures.
Copyright © 2009 Pearson Education, Inc. publishing as Benjamin Cummings
Methane, Plants and Climate Change
Biology and Society
When the media misinterprets scientific findings, it is the
fault of scientists, who should have explained the
meaning of their work more clearly.
Strongly
Disagree
A
B
C
Copyright © 2009 Pearson Education, Inc. publishing as Benjamin Cummings
D
E
Strongly
Agree
Methane, Plants and Climate Change
Thinking About Science
Calculations show that in terms of global warming, the
positive effect of carbon sequestration by reforestation
outweighs the negative effect of methane production by
plants. In addition to knowing the amount of carbon taken
up by growing trees, what else would you need to know to
make these calculations? (Hint: more than one answer
may be correct.)
a) The amount of methane produced by growing trees.
b) The relative heat-trapping properties of carbon
dioxide and methane.
c) The growth rate of trees in different global regions.
d) The current rate of world-wide temperature increase.
Copyright © 2009 Pearson Education, Inc. publishing as Benjamin Cummings
Methane, Plants and Climate Change
Thinking About Science
Calculations show that in terms of global warming, the
positive effect of carbon sequestration by reforestation
outweighs the negative effect of methane production by
plants. In addition to knowing the amount of carbon taken
up by growing trees, what else would you need to know to
make these calculations? (Hint: more than one answer
may be correct.)
a) The amount of methane produced by growing trees.
b) The relative heat-trapping properties of carbon
dioxide and methane.
Copyright © 2009 Pearson Education, Inc. publishing as Benjamin Cummings
Methane, Plants and Climate Change
Interpreting Charts and Graphs
What conclusion can be drawn from comparison of the two graphs?
a) There has been no change in the amount of biomass burned.
b) The amount of methane produced from wetlands has increased.
c) There are fewer termites in modern times.
d) There was more burning of biomass in preindustrial times.
Copyright © 2009 Pearson Education, Inc. publishing as Benjamin Cummings
Methane, Plants and Climate Change
Interpreting Charts and Graphs
What conclusion can be drawn from comparison of the two graphs?
b) The amount of methane produced from wetlands has increased.
Copyright © 2009 Pearson Education, Inc. publishing as Benjamin Cummings