Tag Archives: climate change

Carbon Cycle Consequences of Vegetation/Climate Mismatch

Posted on by
3

David P. Turner / September 15, 2023

Planting a tree should include a species selection process that factors in projected climate change over the lifetime of the tree.  Image Credit.

Equilibrium between vegetation and climate refers to the state in which the species and ecosystem type best adapted to a particular area actually occupy that area.

At a geologic time scale, Earth’s climate is always changing and as climate changes, the best adapted species for a given geographical area likewise changes.  However, for a variety of reasons, the arrival and establishment of the best adapted vegetation may lag behind the climate change.  Biogeographers refer to vegetation/climate disequilibrium in this case.

Note that achieving vegetation/climate equilibrium may take hundreds to thousands of years, so the faster climate is changing, the less likely it is that the vegetation will remain in equilibrium with it.

The Holocene Epoch (from about 11,000 B.P. to present) was characterized by a relatively stable climate, and global vegetation has mostly equilibrated with the climate.  But now we have entered the Anthropocene epoch in which anthropogenic greenhouse gas emissions are driving a high rate of climate warming.  Consequently, long-lived vegetation is beginning to fall out of equilibrium with the climate over wide swaths of the terrestrial surface (albeit that humans have already massively altered global vegetation).

As the disequilibrium gets greater, forests in particular become more stressed and vulnerable to disturbances such as insect outbreaks and fire.

The incidence of fire is already increasing around the world because of climate change and we can expect that trend to continue.  For example, my simulations of vegetation change in the Willamette Basin (Western USA) project a several fold increase in the incidence of forest fire in coming decades as the climate changes.

The carbon cycle consequences of a growing vegetation/climate disequilibrium are significant.

1.  More fires mean more direct emissions of CO2 and more woody residues (dead trees), which will eventually decompose and emit CO2.  Local photosynthesis (CO2 uptake) is reduced in recently burned areas until the vegetation leaf area recovers.

2.  Forests stressed by climate change are increasingly vulnerable to pests and pathogens.  As with fire, associated damage to trees reduces growth and may cause mortality, and the residual dead trees gradually decompose and return CO2 to the atmosphere.

3.  Climate change is increasing Vapor Pressure Deficits (the drying power of the atmosphere), which tends to reduce stomatal opening and hence reduce photosynthesis and uptake of CO2.  Plant species are adapted to a specific range of VPD and can die when VPDs exceed their tolerance.  Interestingly, the increasing concentration of CO2 from fossil fuel emissions compensates to some degree for VPD-induced stomatal closure because CO2 diffusion into the stomata increases as the concentration gradient between leaf exterior and interior rises.  The net effect of these opposing factors varies geographically depending on many variables.

The global impact of increasing disequilibrium between vegetation and climate on the carbon cycle is concerning because it will likely reduce the current terrestrial carbon “sink”.  At the global scale, the net effect of biological carbon sources and sinks on land is a carbon uptake equivalent to about 29% of fossil fuel emissions.  Much of that carbon accumulation is in wood and soil.  The effects of vegetation/climate disequilibrium may reduce the current rate of land-based sequestration, which would leave more fossil fuel-based CO2 emissions in the atmosphere.  The annual increase in atmospheric CO2 concentration has increased in recent decades (Figure 1), mostly because of increasing fossil fuel emissions.  In the absence of strong emissions reductions, any draw down of the terrestrial sink will tend to further increase that annual uptick in concentration.

Silvaculturalists must have a long planning horizon and some have already begun to factor in vegetation/climate equilibrium in their tree planting prescriptions.  They use spatially-explicit projections of climate change from global and regional climate models, along with studies of tree species’ distribution based on historical climate.  Given the high certainty of long-term climate change, anyone who plants a tree in the coming decades and centuries  ̶  for wood production, climate change mitigation, or various other good reasons  ̶  should attempt to account for projected climate change over the lifetime of the tree.

Figure 1.  Mean annual carbon dioxide growth rate.  Bars are the decadal averages.   Image Credit NOAA.

Six More Rationales for Supporting a Renewable Energy Revolution

Posted on by
Reply

David P. Turner / May 12, 2022

The threat of global climate change points to the dire need for a renewable energy revolution in which energy from combustion of fossil fuels (coal, oil, natural gas) is rapidly displaced by energy from renewable sources (wind, solar, geothermal, hydro).  Research by engineers and economists attests to the feasibility of building a global energy infrastructure that runs on renewable energy.  However, forward looking policies must be designed and strong political will must be generated.

In a heavily politicized environment such as Washington D.C., policies are much more likely to get implemented when they are supported for more than one reason.  The underlying mechanism is that with powerful forces aligned for and against any given policy proposal, several constituencies  ̶  each supporting a desired policy for a different reason  ̶  must coalesce to overcome opposition.

Clearly, the strongest rationale for a global renewable energy revolution is to reduce greenhouse gas emissions and mitigate climate change.  But here are six additional rationales that should motivate leaders and legislators to support renewable energy policies.

1. Geopolitical strategy.  The Russian invasion of Ukraine has thrown a spotlight on the vulnerability of nations to energy blackmail.  Domestic production of renewable energy reduces dependency on imported fossil fuels and gives a nation greater flexibility in foreign policy.  Many countries in the European Union are now ramping up renewable energy production in the face of threatened cut-off of fossil fuels from Russia. 

2.  The cost of renewable energy is decreasing.  Renewable energy is already cheaper than fossil fuel energy in some cases, and technological advances in generation, storage, and distribution will continue to drive down costs.  Each time a component of the global fossil fuel infrastructure ages to the point of needing replacement, a decision must be made to continue burning fossil fuel or switch to renewables.  From a purely economic perspective, the better decision may be to go with renewable energy.

3.  The cost of fossil fuels is increasing.  Currently, much of the environmental and social costs of fossil fuels are externalized, but as those costs begin to be covered by more stringent regulation and carbon taxes, the overall costs of fossil fuels will be pushed up.

4.  Public health.  Combustion of fossil fuels results in emissions of nitrogen compounds and hydrocarbons that participate in the formation of harmful ground-level ozone and particulates (Figure 1).  A long history of research and monitoring by environmental agencies supports the conclusion that ground-level ozone is detrimental to human and crop health.  The non-climate related economic benefits of reducing fossil fuel combustion (e.g. reduced sickness and death from air pollution) exceed the climate-related benefits in the early decades of greenhouse gas mitigation scenarios.

smog at sunset
Figure 1. Impacts of air pollution on human health and vegetation drive support for a global renewable energy revolution. Image Credit: jplenio from Pixabay

5.  Nitrogen deposition.  The nitrogen compounds associated with fossil fuel combustion eventually fall out of the atmosphere in precipitation or as dry deposition. This excess nitrogen is deposited to terrestrial, aquatic, and marine ecosystems and drives eutrophication and soil acidification.

6.  Job creation.  Building and maintaining an expansive renewable energy infrastructure will create on the order of seven times more jobs than will be lost from the fossil fuel and nuclear industries as they recede.  The issue of job creation will become increasingly important in the coming decades as computer-driven artificial intelligence displaces human beings.

The multiple rationales noted here for policies that support a renewable energy expansion will hopefully, in aggregate, move the needle away from further investments in the fossil fuel infrastructure.  Policies that stimulate renewable energy technology include subsidies on electric vehicles and residential solar power installation, whereas carbon taxes and regulation of drilling rights on public land can serve to limit fossil fuel development.

Of immediate concern is that a desire to reduce consumption of Russian fossil fuels will be used as a justification for increasing fossil fuel production in the U.S. and elsewhere.  Considering the long turnover time of fossil fuel infrastructure (e.g. 50 years for a coal burning power plant) and the ample opportunities for expanding renewable energy, great caution should be taken with investments that prolong the era of fossil fuels.

The Technosphere is Melting the Cryosphere

Posted on by
Reply
Iceberg in Lilliehöökfjord, Svalbard.  Image credit: Hannes Grobe, CC BY-SA 4.0

David P. Turner / February 1, 2021

Earth system scientists think of planet Earth as composed of multiple interacting spheres.  The cryosphere is a term given to the totality of frozen water on Earth – including snow, ice, glaciers, polar ice caps, sea ice, and permafrost.

The cryosphere has a significant effect on the global climate because snow and ice largely reflect solar radiation, hence cooling the planet.

Unfortunately, the cryosphere is melting.  That loss of snow and ice is providing a significant positive (amplifying) feedback to anthropogenically induced global warming.

Over the course of Earth’s geological history, the cryosphere has existed as everything from nearly 100% coverage of the planetary surface around 700 Mya (million years ago) i.e. snowball Earth (Figure 1) to virtually disappearing during the Hothouse Earth period (about 50 Mya).

Figure 1. Snowball Earth.  The planet was nearly covered in snow and ice around 700 million years ago.  Image Credit: NASA.

The multiple glacial-interglacial cycles over the last several million years were initiated by changes in sun/earth geometry (the Milankovitch cycles), but strengthened by changes in snow/ice reflectance along with changes in greenhouse gas concentrations.

Figure 2.  Ice cover (black) shifted markedly between the glacial and interglacial periods over the last 3 million years.  Image credit:  Hannes Grobe CC Attribution 3.0

The culprit in the current melting of the cryosphere is something new to the Earth system – the technosphere.  This recently evolved sphere consists of the totality of the human enterprise on Earth, including its myriad physical objects and material flows.

By way of fossil fuel combustion, the technosphere is driving up the concentrations of greenhouse gases in the atmosphere and correspondingly, warming the global climate.  That new heat is causing reduced snow cover, receding glaciers, melting of ice caps, and loss of sea ice.  By various anthropogenically driven mechanisms, the cryosphere is also said to be “darkening” and hence melting quicker because more solar radiation is absorbed.

Projections by Earth system models of cryosphere condition over the next decades, centuries, and millennia suggest it will significantly wane if not disappear.

Besides the positive feedback to climate change by way of reflectance effects (and release of greenhouse gases from permafrost melting), the diminishment of the cryosphere will have profound impacts on the technosphere.

  1.  The circulation of water through the hydrosphere on land is regulated in many cases by accumulation of snow and ice on mountains.  That water is subsequently released throughout the year, thus providing stable stream flows for downstream irrigated agriculture and urban use. 
  2. The melting of glaciers and the polar ice caps will drive up sea level.  If all such ice is melted (over the course of hundreds to thousands of years), sea level is projected to rise 68 m.  The magnitude of sea level rise projected over the next 100 years for intermediate emissions scenarios is on the order of one meter.
  3. It remains controversial, but reduction of snow and ice cover may alter the behavior of the jet stream and could induce more extreme weather events in mid- to high latitudes of the northern hemisphere.

Efforts to reduce greenhouse gas emissions will certainly slow the erosion of the cryosphere and should be made.  The precautionary principle suggests we avoid passing tipping points associated with melting of the Greenland ice cap and the Antarctic ice cap.  However, the momentum of environmental change is strongly in that direction.

Once these ice caps are gone, there is a hysteresis effect such that the ice does not return with a simple reversion to the current climate (e.g. by an engineered drawdown of the CO2 concentration).

The planet is headed towards a warmer, largely ice free, condition.  The biosphere has been there before.  The technosphere has not.  Humanity will be challenged to develop adequate adaptive strategies.

Recommended Video: What is the Cryosphere │How it Affects Climate Change

Earth Day 2020

Posted on by
2

Earth Day 2020 and Global Solidarity

David P. Turner / April 19, 2020

Earth Day in 2020 is the 50th Anniversary for this annual gathering of our global tribe.  Historically, it has been an opportunity to note declines in environmental quality and to envision a sustainable relationship of humanity to the rest of the Earth system.

This year, in addition to the usual concerns about issues like climate change and ocean acidification, Earth Day is accompanied by concern about the specter of the COVID-19 pandemic.  A glance at the geographic distribution of this virus is the latest reminder that interactions with the biosphere, in this case the microbial component, can link all humans in powerful ways. 

Environmental issues that were on the front burner when Senator Gaylord Nelson initiated Earth Day in 1970 were mostly local − polluted rivers, polluted air, and degraded land cover.  These issues were addressed to a significant degree in the U.S. by passage of the Clean Water Act (1972), the Clean Air Act (1970), and the Endangered Species Act (1973).  These were national level successes inspired by environmental activism.

Awareness of global environmental change in 1970 was only dimly informed by geophysical observations such as the slow rise in the atmospheric CO2 concentration.  But by the 1980s, climate scientists began a drumbeat of testimony to governments and the media that the environmental pollution issue extended to the global scale and might eventually threaten all of humanity. 

The United Nations has functioned as a forum for international deliberations about global environmental change issues, and the signing of the Montreal Protocol on Substances that Deplete the Ozone Layer in 1987 hinted at the possibilities for global solidarity with respect to the environment.

To help matters, economic globalization in the 1990s began uniting the world in new ways.  Huge flows in goods and services across borders fueled a truly global economy.  The level of communication required to support the global economy was based on the rapidly evolving Internet.  It provided the foundation for a global transportation/telecommunications infrastructure that now envelops the planet.

A political backlash to economic and cultural globalization has recently brought to power leaders like Donald Trump (U.S.) and Jair Bolsonaro (Brazil).  Their inclination is much more towards nationalism than towards global solidarity on environmental issues.

However, humanity is indeed united – in fear of climate change and coronavirus pandemics if nothing else.

Each year, the growing incidence of extreme weather events associated with anthropogenic climate change negatively impinges on the quality of life of a vast number of people around the planet.  This year, billions of us are locked down in one form or another to slow the spread of a virus that likely emerged from trafficking in wild animals.  In a mythopoetic sense, it is as if Earth was responding to the depredations imposed upon it by our species.

Philosopher Isabelle Stengers refers to the “intrusion” of Gaia (the Earth system) upon human history.  The message from Gaia is that she is no longer just a background for the infinite expansion of the human enterprise (the technosphere). 

Humanity can reply to Gaia with ad hoc measures like building sea walls for protection from sea level rise.  Or we can get organized and develop a framework for global environmental governance.

There are many impediments to becoming a global “we” that will work collectively on global environmental change issues.  Nevertheless, the incentives for doing so are arriving hard and fast.  The diminishment of the wild animal trade in China in response to COVID-19, and the unintended reduction of greenhouse gas emissions globally associated with efforts to slow the spread of COVID-19, signal that radical change is possible. 

Fitting testaments to an emerging global solidarity about environmental issues would be eradication of commercial exploitation of wild land animals everywhere in the world, and stronger national commitments to reduce greenhouse gas emissions relative to current obligations under the Paris Climate Agreement. 

Both initiatives of course face strong cultural and political headwinds.  But Earth Day, as one of the largest recurring secular celebrations in the world, is an opportunity to think anew.

Recommended audio/video:
One World (Not Three), The Police
https://www.youtube.com/watch?v=N0U-IaURsGM

Peak Carbon Dioxide Emissions and Peak Carbon Dioxide Concentration

Posted on by
2

David P. Turner / January 11, 2024 (update)

Figure 1.  Projections of CO2 emissions and concentration.  Image Credit NOAA

In 2020, a remarkable speculation circulated in the cybersphere to the effect that global emissions of carbon dioxide (CO2) from fossil fuel combustion may have peaked in 2019.  Considering that recent formal projections generally indicated increasing emissions through 2030 or longer, this assertion was striking.  It matters because CO2 emissions determine the growth in the atmospheric CO2 concentration, which in turn influences the magnitude of global warming.

The atmospheric CO2 concentration is currently around 420 ppm (up from a preindustrial value of around 280 ppm) and is rising at a rate of 2-3 ppm per year.  The consensus among climate scientists is that rapid greenhouse-gas-driven climate change will be harmful to the human enterprise on Earth.  It would be good news indeed if CO2 emissions were on the way down.

Estimates for annual global CO2 emissions are produced by assembling data on consumption of coal, oil, and natural gas, as well as data on production of cement and effects of land use.  The sum of fossil fuel and cement emissions is termed Fossil Fuel & Industry emissions (FF&I).  Land use, land use change, and forestry (LULUCF) is mostly the net effect of carbon emissions from deforestation and carbon sequestration from afforestation/reforestation.  Total anthropogenic emissions are the net of FF&I and LULUCF.  Two independent estimates of CO2 sources and sinks (GCP and IEA) differ slightly.

The suggestion that peak fossil fuel emissions occurred in 2019 held true in 2020 and again in 2021 and 2022, but 2023 saw a 1.1% increase over 2019. 

Intriguingly, a decline in LULUCF compensated for the increase in fossil emissions such that total anthropogenic emissions remained the same in 2023 as 2022 (11.1 GtC yr-1).  That result may hold in 2024 as well if President Lula of Brazil continues to succeed in reducing deforestation, and global fossil fuel emissions grow only modestly (if at all).

Several specific observations points towards lower emissions in the near-term future.

1.  Global coal emissions declined from 2012 to 2019 but have risen above 2012 in recent years, primarily due to increases in India and China.  However, coal emissions declined 18.3% in the USA and  18.8% in the EU in 2023.  Aging coal powered electricity plants in the U.S. are being replaced with plants powered by natural gas (more efficient that coal) or renewable energy.  Some coal plants have been prematurely retired.  A gradual phase out in global coal consumption is being driven by the price advantage of renewable energy, impacts of coal emissions on human health, and the reluctance of insurance companies to cover new coal power plant construction.  China has agreed to stop financing the construction of coal power plants in developing nations and India has pledged to stop approving new domestic coal plants.

2.  Peak oil use may have occurred in 2019.  Global demand in 2020 fell 7.6% because of Covid-19. It partially recovered in 2021 and 2022 and 2023 but remains below the level in 2019.  Structural changes such as reduced commuting and business-related flying mean that some of the demand reductions associated with Covid-19 have persisted.  Vehicles powered by electricity and hydrogen rather than gasoline are on the ascendancy, sparked in part by governmental mandates to phase in zero emissions vehicles.

3.  Even a near-term peak in natural gas consumption is being discussed.  The GCP budget for 2022 showed a 0.2% decline in gas emissions and for 2023 a 0.5% increase.  Again, the price advantage of renewable sources will increasingly weigh against fossil-fuel-based power plants.  The growing importance of energy security at the national level also argues against dependence on imported fossil fuels.  Ramped up production of renewable natural gas could substitute for fossil natural gas in some applications.

It is likely that the approaching peak in total fossil fuel use will be driven by diminishment of demand rather than lack of supply.

Currently about half of FF&Iemissions remain in the atmosphere, with the remainder sequestered on the land (e.g. in vegetation and soil) and in the ocean.  The land sink is increasing in response to 1) high CO2 enhancement of photosynthesis and plant water use efficiency, and 2) policy driven impacts on land management (e.g. more reforestation and afforestation).

Once fossil fuel emissions begin decreasing and fall by half − and assuming the net effect of increasing CO2 and climate warming is still substantial carbon uptake by the land and ocean − the atmospheric CO2 concentration will peak and begin to decrease.  The year of peak CO2 concentration could be as early as 2040 (see carbon cycle projection tool below).

On the other hand, there is plenty that might go wrong with this optimistic scenario.  As climate change intensifies, the net effect on land and ocean sequestration could be a decline in carbon uptake.  On land, carbon sources such as permafrost melting and forest fires will be stimulated by climate warming.  In the ocean, warming will intensify stratification, thereby reducing carbon removal to the ocean interior.  The steady increase in the ocean carbon sink since around 2000 has stalled in recent years, for poorly understood reasons.  If fossil fuel emissions are not significantly abated in the coming decades, the CO2 concentration could still be rising in 2100 (Figure 1).

Recommended:  Interactive CO2 Emissions and Concentration Projection Tool.