New report in the Journal Nature has revealed details on a very common and erroneous assumption on where water vapour comes from in the atmosphere.
This has dramatic consequences on its role as a greenhouse gas. Virtually every reference on climate states that the largest source of atmospheric water vapour is evaporation.
The new Nature paper by Scott Jasechko et al shows the common idea that water vapour in the air mostly comes from evaporation is wrong. Jasechko shows that in fact 60% of atmospheric water vapour comes from plant transpiration and only 40% from evaporation! (Read a related post here.)
Since water vapour is by far the most important of all greenhouse gases, representing 66%-72% of the GHG effect this is very important to the models that forecast global warming and climate change. CO2 owns a 20%-26% share of global warming. Many are now trying to understand why climate models have failed to account for the recent slowing of global warming. The answer to this dilemma may be one of the dramatic breakthroughs that derives from the Jasechko report.
A second striking detail revealed in Jasechko’s paper is that our high and rising CO2 is dramatically driving plant photosynthesis efficiency and enormous reductions in plant transpiration.
This new view of the role of plants in regulating the climate is where things get really powerful. Since water vapour is the primary “Green House Gas” (GHG) making up 66%-72% of the greenhouse effect a small change in water vapour can drive a big change in global warming.
Indeed based on this new report the decline in water vapour in the atmosphere due to the beneficial effect of high CO2 on plants is perhaps 10% or more. That means that we ought to be seeing a reduction of the global warming forcing effect of the water vapour GHG of about 6% -7%.
The numbers are remarkably close to those needed to explain recent slowing of global warming, or as some might say global cooling, taking place in spite of rising CO2.
In the past 20 years, since 1992, CO2 concentration in the air has risen by 10%.
That should have driven something like ~3% or a ~0.3Cº additional warming effect, but that warming has not been observed. Something is amiss in the models.
That missing global warming is easily accommodated within the CO2/plant regulated cooling effect of 6.6% or more! The coincidence of this simple explanation calls for the invocation of Occam’s Razor, “when you have two competing theories that make exactly the same predictions, the simpler one is the better.”
But here is yet another twist on the potency of fossil CO2. Rising CO2 has an even more powerful GHG effect in powering diminished plant transpiration and thus slowing of water vapour GHG effects.
It just goes to show us that the real power on this planet are the plants.
While the CO2 feedback effect on diminished global warming due to terrestrial plant enhancement is a big factor where high and rising CO2 modifies plant life it’s not alone. Perhaps an equal or even greater role of CO2 on impacting plants is in the ocean plankton pastures where the vast majority of earthly plant life grows. For ocean plants the most important effect of terrestrial plant enhancement by high and rising CO2 is that those water saving, bushier, greener, longer living land plants are what we call “good ground cover.”
Good ground cover does just that, it covers the ground and prevents soil from blowing in the wind. The diminished dust in the wind is a devastating loss of vital mineral micronutrients suppressing ocean phytoplankton. This is born out in many papers in the ocean sciences which report drastic declines in ocean plants. At least 1% per year of all ocean plant life has been disappearing since 1950 (Worm et al.)
How much is this in the context of terrestrial plant life, it is a loss of plant biomass in each five-year span as if an entire Amazon Rainforest were destroyed. New reports Martiny et al are now showing double the amount of carbon in ocean ecosystems, this could mean we have been losing twice the number of rainforests in each five year span!
That’s a dozen Amazon Rainforests eradicated since that 1950 date. That amount of plant photosynthesis was removing a vast amount of CO2 from the atmosphere. A deadly feedback loop with respect to CO2 and its role in controlling photosynthesis and hence global warming and climate change.
Add these three synergistic effects into any climate change model and one is likely to see a very near coincident explanation with the observations of global temperature measurements and trends.
This does NOT mean that CO2 has diminished role in global warming and climate change. It means CO2 has a far more potent role through its biological action. And we all always knew that the biological potency of CO2 far exceeded its mere physical character as are used in climate models.