Category Archives: Short Form

Earth Day 2023 and Global Solidarity

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David P. Turner / April 16, 2023

Earth Day 2023 (April 22) is the 53rd anniversary for this annual gathering of the global tribe.  Historically, it has been an opportunity to protest the decline in environmental quality and to envision a sustainable relationship of humanity to the rest of the Earth system.

So, let’s review three environmental trends of particular concern in 2023 and three pointers to the possibility of a sustainable Earth system.

Three concerns.

1.  2023 is shaping up to be an El Niño year.  Ocean circulation in the equatorial Pacific Ocean will slow, which means less heat removal to the ocean interior by downwelling water in the western pacific and less delivery of cool upwelling water in the eastern Pacific.  Global mean temperature will tick up a bit beyond the usual expectation.  There is speculation that 2023 will be the warmest year on record.

2.  Sea ice extent will continue to decline at both poles, which is part of the snow/ice albedo positive feedback to global warming.

3.  Greenhouse gas concentrations will continue to rise.  The annual increase in methane concentration is especially worrisome because the increase has been relatively large in recent years, a consequence of rising emissions from both the global energy sector and biosphere sources.

Three trends to be hopeful about.

1.  The International Energy Agency recently reported that 2023 will mark a step-change upward in the public and private financing available to support the global renewable energy revolution.  The official theme of Earth Day 2023 is “Invest in Our Planet”.

2.  The proportion of land and ocean area in some sort of biodiversity protection status continues to rise.  A 2022 UN biodiversity conference set a goal of 30% by 2030.

3.  Stratospheric ozone continues to regenerate in response to the global regulatory process associated with the Montreal Protocol.

There are endless issues within countries and between countries for humans to argue and fight about.  But recent anthropogenically-driven changes in the global environment are something we all have in common, and something that must be addressed collectively.

In the near term, 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.  On a decadal time frame, sea level rise will come to displace hundreds of millions of people.  At the scale of a century or more, on-going climate change may set off a cascade of positive feedback mechanisms that will drive the Earth system to a new state inimical to an advanced, high technology, global civilization (the Icarus Scenario).

There are many impediments to becoming a global “we” that will work collectively on global environmental change issues.  But Earth Day, as the largest recurring secular celebration in the world, is an occasion to think anew and commit to opportune joint initiatives.

We’re Going to Need a Bigger Power Supply and It Better be Renewable

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David P. Turner / March 1, 2023

Developing and maintaining AI-based conversational beings ̶ such as ChatGPT ̶ will significantly increase global energy demand. In the interests of global sustainability, that additional power must be from renewable sources. Original graphic (Monica Whipple and David Turner).  Image Credits: Circuitry, Wind Farm, Solar Panels, Pylons.

When the sheriff character in the original “Jaws” movie first sees the giant shark, he exclaims to the captain “You’re gonna need a bigger boat”.

An analogous statement regarding the energy requirements associated with the coming proliferation of conversational virtual beings (based on Artificial Intelligence) is that the technosphere is going to need a bigger power supply.

By virtual beings I mean all the digital, language-capable, denizens of the emerging metaverse (broadly defined), including chatbots (like ChatGPT), AI-assisted search engines (like Perplexity AI), and AI-based residents of Meta’s visor-enable virtual reality world.  Coming down the line are speaking holograms, and holodecks (as in Star Trek).

The process by which these advanced digital creatures learn to speak is based on development of neural networks that are trained with a large body of textural information (like Wikipedia, books, and an array of content available on the Internet).  Training means determining statistical relationships between the occurrence of different words in the training text, which the algorithm then uses to formulate a response based on keyword inputs (queries).

Training a large language model such as ChatGPT requires a hefty input of computing power because it involves extensive trial and error testing.  Chatbots affiliated with AI-assisted Internet searches use not just a pre-trained language model but also integrate the search output into their responses.  This kind of processing will be energy demanding (perhaps 5 times greater than for a standard search), which will add up considering the billions of searches made per day.

If these virtual beings were only going to be used by a minority of people (such as now visit Meta’s colony in the metaverse), the power draw would be minor.  But, very likely, their seductive appeal will be so great (albeit with an occasional hint of menace) that they will become a standard feature of ordinary life.  Just in the field of education, there is vast potential for inspiring and informing students using dialogic Chatbots.

Efficiency in training and operation of these virtual beings will no doubt increase, but industry specialists see a booming rise in electrical energy demand as their use expands.  Note that electrical power demand for electric vehicles, and to power the broader trend towards electrification of heating and industry, will also rise significantly in the coming decades (a good thing!). 

The overshoot model argues that global energy consumption should be reduced rather than expanded because of the many negative environmental externalities (unaccounted for damages) caused by energy production  ̶  from both fossil fuel and renewable sources. 

However, at least for electricity, that seems unlikely given the burgeoning energy demand in the developed world noted here, and the aspiration to raise standards of living in the developing world.

Since 66% of global electricity production is still based on combustion on fossil fuels, any increase in electricity consumption will tend to result in more greenhouse gas emissions and more societal problems with climate change.  The obvious conclusion in that new energy demand must be met by nonfossil fuel sources like hydro, wind, solar, geothermal, and nuclear fission.  Companies such as Google, Microsoft, and Meta that are building the metaverse will experience huge increases in energy consumption in the near future; they should be held to their commitments to run on carbon neutral power sources.

New energy technologies that could contribute to a clean global power supply in the coming decades include geologic hydrogen and solar energy from space.  These sources, however, will require long-term investments in research and development.

The global renewable energy revolution is off to a good start and has a bright future, but it will require steady political pressure to 1) stop building new fossil fuel burning facilities, 2) replace aging fossil-fuel-based infrastructure with renewable sources, and 3) build new renewable energy sources that can accommodate the increasing demand that is surely coming.

Decarbonizing the Power Sector

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Figure 1.  Design for a decarbonized utility scale electrical power facility.  Image credits: solar array, electrolyzer, hydrogen storage, hydrogen fuel cell, power grid

David P. Turner / November 11, 2022

National governments the world over have made political commitments to reduce greenhouse gas emissions significantly in the next few decades.  Because the generation of electricity, i.e. the power sector, is currently one of the largest anthropogenic sources of CO2 emissions (due to its reliance on coal and natural gas burning power plants), a great deal of research and investment is directed towards power sector decarbonization.

There are many pieces to the technical puzzle of how to decarbonize the power sector, and the optimum answer will differ depending on location and available resources.  But generating electricity while avoiding fossil fuels altogether is entirely feasible.

In that regard, I was happy to see news of a funded power project that nicely weaves together many of the critical components needed to deliver carbon-free electricity at grid scale (Figure 1).

The facility in this case is being built in French Guiana by a consortium of private firms.  The exciting thing to see is the co-location and integration of five key power generation components:  (1) an array of solar panels, (2) an electrolyzer to produce hydrogen, (3) a hydrogen gas storage capability, (4) a hydrogen fuel cell that generates electricity, and (5) a short-term battery energy storage system.  Functioning together, these components will provide a 24/7 baseload supply of carbon free electricity (10,000 households worth).

The solar array collects sunlight.  Most of the energy is fed into the local electricity grid, but a portion is directed to the electrolyzer to split water molecules into oxygen and hydrogen.  The hydrogen gas is stored on site.  At night, the hydrogen is supplied to the fuel cell generator.  The short-term battery storage system helps maintain a steady flow of energy as needed.

This kind of facility largely solves the intermittency problem for renewable solar energy.  Its design could be adapted to other renewable energy sources with an intermittency problem, notably wind energy farms.  Excess hydrogen could potentially be transported to other locations by pipeline or in liquid form.

Successful operation of the facility (slated to open in 2024) will provide a model that potentially could be scaled up and widely adopted.  Since garnering the political will and financing for renewable energy development is still a significant challenge, the completion and operation of this power plant would send of strong signal about the feasibility of decarbonization to government, industry, and sources of investment.

News that this facility is actually under construction inspires the feeling that the global we (such as it is) can indeed accomplish a needed renewable energy revolution.

More Blows to Humanity’s Self-image

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heliocentric universe
Cellarius’s chart (1661) illustrating a heliocentric model of the universe, as proposed by Nicolaus Copernicus.  Image Credit.

David P. Turner / October 2, 2022

Copernicus, Darwin, and Freud are credited with delivering major blows to humanity’s self-image. They didn’t do it on their own of course, but their ideas were notably illuminating.  Here, I revisit their insights and discuss two additional blows of that type rendered in more recent years.  Awareness of the human limitations implied by these blows may help save us from our present environmental predicament.

Copernicus (1473 -1543) established that – contrary to Church dogma – Earth rotated on its axis and revolved around the sun.  Humans could no longer maintain that we are living at the center of the universe.  The scientific discipline of astronomy has gone on to reveal how remarkably tiny this planet really is in the context of an immense universe.  Knowing that we live on a small planet points to biophysical limits on our current demands for natural resources.

Darwin (1809 – 1882) elucidated the theory of biological evolution, and the corresponding fact that Homo sapiens originated the same way every other animal species on this planet did – through natural processes.  We were no longer a special creation of an omnipotent, benevolent god who dictates our aspirations and values.  Ironically, though, humanity is coming to have a kind of dominion over the Earth even without the hand of god.

Freud (1856 – 1939) suggested that unconscious processes within our brains have a substantial influence on our thoughts and emotions.  He turned out to be wrong in many respects, but his primary insight had merit.  We are not even in full control of our own minds.  Contemporary cognitive science aims to understand (1) the function (adaptive significance) of specific mental processes, (2) the representations and algorithms by which those processes are implemented, and (3) the underlying neurobiological mechanisms.  Insights along those lines may help modify our destructive impulses.

The two recent blows to our self-image come from a biologist and an atmospheric chemist.

In the 1970s, Harvard professor E.O. Wilson (1929 – 2021) fostered the development of the new discipline of sociobiology – the study of animal social behavior.  He applied its concepts to Homo sapiens, as well as to ants (his favorite object of study).  What he asserted (albeit in the face of raging controversy) is that humans have significant genetic influences on our thinking and behavior.  Our capacity for altruism (self-sacrifice) and jealousy are notable example of traits which evolution has likely shaped.  As with the first three blows, this realization forces us to question our spontaneous motivations and actions (e.g. our acquisitiveness).

The fifth blow is truly aimed at the whole of humanity.  Around 2000, atmospheric chemist Paul Crutzen (1933 – 2021) helped consolidate a wide array of observations by Earth System Scientists concerning the baleful influences of humanity on the biosphere and the global environment.  He suggested that we have entered a new geologic epoch – the Anthropocene. 

In the scientific Anthropocene narrative, humanity has become the equivalent of a geologic force; we are now capable of significantly altering the global biogeochemical cycles.  This shocking realization and consequent shift in worldview have been characterized as the “second Copernican revolution”.

Unfortunately, we are altering the global environment in a way that may ultimately be self-destructive (e.g. by inducing rapid global climate change).  Our self-image must therefore include the conclusion that we are an existential threat to ourselves.

Recognition of the Anthropocene epoch places a new responsibility on each of us as individuals, and a new responsibility on our species as a whole, to begin managing ourselves – and to some degree begin managing the Earth system – in support of global sustainability.

The prescription for better integration of the human enterprise (the technosphere) with the Earth system requires that humanity become aware of itself as a social entity, having agency at the global scale, before it can learn to self-regulate and reintegrate with the Earth system.  Awareness of the five blows covered here introduces an element of humility to this project of understanding ourselves as a planetary phenomenon.

Environmental Reglobalization

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David P. Turner / April 24, 2022

Globalization refers to the increasing interconnectedness of individuals and social groups everywhere on the planet, and to the increasing inability of any particular social group to isolate itself from outside influences.  The process has geopolitical, economic, cultural, and environmental dimensions. 

In this post, I am particularly interested in how globalization, and its follow-on stages of deglobalization, and reglobalization, impact the global environment (Figure 1).

three stages of globalization
Figure 1.  Three sequential phases of globalization.  Neoliberal globalization from around 1980 to 2008 was based on maximizing profits by way of free trade within a global capitalistic system.  More recently, nationalistic deglobalization is characterized by a reassertion of national borders and reduction in flows of trade goods, financial capital, and immigrants.  Environmental reglobalization is a potential way forward in which the necessity to collectively address global environmental change issues provides a basis for global solidarity.  Image Credits: Neoliberal Globalization, Nationalistic Deglobalization, Environmental Reglobalization, Composite (D. Turner).

Despite globalization’s significant detrimental impacts on the global environment – notably a large stimulus to growth in the global Gross Domestic Product and associated greenhouse gas emissions – it has also had significant beneficial effects on the global environment, e.g. progressive environmental standards have been widely promulgated, and a global environmental governance infrastructure has begun to function.

However, globalization is currently in retreat, and any possible environmental benefits from it are in jeopardy.  Causes of the current wave of deglobalization include: 1) the economic suffering imposed on workers in the most developed countries by globalization of the labor market (which has inspired efforts to reduce imports of manufactured goods), 2) the psychological shock of juxtaposing very different cultures (e.g. secular vs. religious) made possible by modern transportation and communication technology (hence leading to revivals of xenophobic fundamentalism), and 3) the political benefits to autocratic leaders from rousing nationalist fervor (hence leading to outbreaks of war, as in Ukraine).

The rise of nationalism and deglobalization is associated with a retreat from global environmental change issues, e.g. the withdrawal of the U.S. from the Paris Climate Agreement by the Trump administration in 2017, and the anti-environmental policies of the Bolsonaro administration in Brazil.  That kind of nationalism shirks responsibility for planetary scale problems and in practice is a false nationalism.  It ultimately endangers all nations on Earth as the global biophysical environment deteriorates and ecosystem services to humans are lost.

Reformed globalization (reglobalization) is a new concept that could help overcome the dangers of deglobalization.  Reglobalization would include stronger national and international efforts to reduce economic inequality and to extend the benefits of globalization more uniformly.  It would mean a wide recognition that we live on a crowded planet, which must be managed collectively to insure continued delivery of nature’s services.  Indeed, global environmental change issues could be the major driver towards an era of greater global unity.

With respect to the environment, reglobalization would include stepped-up green-tech transfer to developing countries for mitigation of climate change, stronger institutions of global environmental governance, and a revived commitment by individuals, institutions, and nations to global sustainability.

Environmental reglobalization will likely not have the prodigious force of the neoliberal globalization wave that began in the 1980s.  Rather, it must be cultivated based on wide public awareness, active civil society organizations, and wise political leadership.

Celebrating the Solstice

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Stonehenge on the Summer Solstice. Image credit: //commons.wikimedia.org/wiki/File:Stonehenge_(sun).jpg

David P. Turner / June 13, 2021

Every human being on the planet will experience an astronomical event on June 20 (2021).  I refer of course to the June Solstice, the point in Earth’s orbit around the sun when daylength begins to shorten in the northern hemisphere and to lengthen in the southern hemisphere.  The astronomical orientation is reversed in the December Solstice.  Our ancestors were very attuned to these annual events, as evinced by the alignment of the megaliths at Stonehenge and at other ancient observatories.  Most Earth dwellers now live urban lives and may give little thought to the orientation of Earth to Sun.  I propose thinking about Solstice events in a new way – as a celebration of planetary citizenship.

Especially since the late 1980s, scientists have produced a drumbeat of reports documenting a range of global environmental change threats, notably climate change.  The sum of environmental impacts from 7.8 billion people is driving the Earth system towards a condition that will cause vast human misery, and perhaps imperil civilization itself.  Humanity clearly must begin to act collectively to mitigate our impacts on the environment.  But we live in a world that is highly polarized and seemingly getting more so.

Humans are social animals, and generally identify with a circumscribed social group.  However, because global scale problems require global scale solutions, we Earthlings must now begin identifying with humanity as a whole − quite a challenge for a species whose social instincts evolved when social groups were small bands of hunter gatherers.  A unifying feature of a society is its shared culture, including myths, beliefs, and rituals.  The new importance of the Solstice lies its contribution to an emerging global culture. 

Several features make the Solstice a unifying event.  One is that it is clearly a global phenomenon: everyone experiences it (albeit more strongly at high latitudes).  The celestial mechanics of the Solstice are fairly simple, and contemplating the event stimulates thinking about global scale structures and processes − something which we certainly need to be doing to address the environmental challenges ahead.  

A second relevant feature is that our understanding of the Solstice is science-based.  Whereas the early celebrants at Stonehenge knew from their long-term observations only that the sun had reached its northernmost circuit on Summer Solstice or was beginning its return from the south on Winter Solstice, we can chart Earth’s orbit around the sun and understand that our planet is tilted on its axis, hence the pattern of seasonality.  More broadly, we understand Earth’s climate system and how it is regulated by solar geometry, as well as greenhouse gases in the atmosphere.  For the purposes of a needed common belief system, the scientific worldview wonderfully fits the bill.  The advance of science now provides a growing intellectual heritage that all of humanity can share.

As to how the Solstice might be celebrated, most people on Earth can walk outdoors at sunrise or sunset on June 20th and note where on the horizon that the sun appears or disappears.  The time of day and angle on the horizon are different at every location on Earth, but we all know it is a special day for the planet. 

In a complimentary sense, this action would also help invigorate the local sense of place.  Every year at any location, the two Solstice events will repeat − kind of a comfort really. 

Traditional ways of celebrating the Solstice include decorating trees and lighting candles (Scandinavia).  Occasionally, the media take notice.  This year, wish everybody a happy solstice!  Perhaps we can eventually make it a global holiday.

In this era of growing nationalism and anti-globalization, when the gathering storm of global environmental change means that the society composed of all humanity should be strengthening rather than weakening, we must search for unifying experiences and beliefs.  Attending to the Solstice, be it the one in June or the one in December, is a way to relate to our planetary home and be reminded that we are all in this together.  

Recommended Audio: Seasons by the Steve Miller Band.

The Technosphere is Melting the Cryosphere

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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

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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

Ocean Photosynthesis May Be Decreasing

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My previous blog post noted that global land photosynthesis is clearly increasing in recent decades.  However, when we turn to the ocean, the story is different (albeit more ambiguous).

About half of global photosynthesis takes place in the ocean.  Much of the resulting biomass production (net primary production) is consumed, thus supporting a food web that includes large marine animals like fish and whales.  Billions of people eat wild caught ocean fish each day as a source of protein.

Photosynthesis in the ocean is frequently constrained by nutrient availability.  Hence, areas where photosynthesis is high are often where upwelling brings nutrient-rich deep water to the surface, or runoff from the land includes nutrients. 

Earth system scientists now monitor global ocean photosynthesis using a combination of satellite remote sensing, direct measurements, and modeling.  As always with global scale processes, there is significant uncertainty about the estimates and some regions show increasing net primary production (NPP) while other regions show decreases.  Various studies have reached differing conclusions about trends in the global total, but a recent study suggested that ocean NPP is in decline (1998 – 2015).

Figure 1.  Trend in ocean primary production.  Estimates are based on a biogeochemical model (coupled to a full ocean model) that assimilates ocean color satellite data. 

Oceanographers are beginning to get an understanding of what is driving the decline.

A key factor appears to be reduced delivery of nutrients to the ocean’s surface.  The causes are related to global warming, a process driven by rising concentrations of greenhouse gases in the atmosphere. 

An important mechanism that is slowing delivery of nutrients to the surface ocean is an increase in stratification associated with the general warming of ocean surface waters.  A cap of warm water tends to reduce vertical mixing, which in turn reduces recharge of surface nutrients from deeper waters where much decomposition and nutrient release takes place.

Figure 2.  Trend in ocean mixed layer depth.  Estimates are based on a global physical three-dimensional model of the ocean driven by geophysical observations.

Another process related to nutrient supply involves the cycling of water from the surface to the deep ocean and back to the surface (the thermohaline circulation).  The descending arm of this Earth-girdling loop of ocean circulation is based on warm water brought north by the Gulf Stream.  That water cools, densifies, and sinks in the North Atlantic Ocean and eventually returns to the surface elsewhere bringing with it nutrients from the deep ocean.  Recent measurements suggest a weakening of that descending arm cause by a freshening of North Atlantic waters driven mostly by melting of the Greenland ice cap.

A decline in ocean photosynthesis − the base of the ocean food chain − likely translates into lower fish production.  Fisheries all over the planet are already under stress from many factors, not least of which is overharvesting.  Ocean warming causes decline of coral (a source of NPP), ocean acidification reduces NPP of calcifying plankton, decreases in ocean oxygen from reduced mixing and excess nutrient runoff (coastal dead zones) force fish to migrate, and toxic waste inputs (including macro-, micro-, and nano- plastics) reduce feeding efficiency.  After decades of fish harvest increases, the global catch peaked in the 1990s.  Model-based projections of ocean animal biomass suggest continuing declines with further ocean warming.

Despite the immensity of the ocean, human impacts on it are piling up.  A new narrative about ocean management is needed.

We (as a part of the technosphere) cannot directly change ocean circulation in an attempt to restore declining primary production and fish production.  We can only slow the emissions of greenhouse gases, which would slow global warming and its associated impacts on ocean mixing and circulation.  Stabilizing, then reducing, the atmospheric CO2 concentration would also slow ocean acidification.

The time is now to support leaders who understand the realities of global environmental change and are committed to working domestically and internationally to implement policies that change the current trajectory of the Earth system.