Wind project
This is a 17.5 MW wind project, consisting of 18 wind farm sites in the Indian states of Tamil Nadu, Maharashtra, Rajasthan and Karnataka. (Photo credit: Land Rover Our Planet / Flickr)

Like an earthquake rumbling down the San Andreas Fault, Jeff Gibbs’ and Michael Moore’s controversial film “Planet of the Humans” tore a rift through the environmental movement, a rift its leaders would not yearn for in an election year. After activists have spent decades painstakingly building popular support for climate policies focused on developing and deploying low-carbon technologies, the film and its defenders dismiss these as false solutions, saying the focus should instead be on curbing population, consumption, and economic growth.

Both those factions agree that, as the IPCC has concluded, human civilization must cut its carbon emissions to zero within a few decades to avert a climate crisis. Is there a scientific way to determine which group is right about the best way to achieve that goal? As a matter of fact, there is.

Kaya formula

In 1990, Japanese energy economist Yoichi Kaya developed a simple and elegant formula called the Kaya Identity that can help answer the question: F is human carbon emissions, P is human population, G is economic activity as measured by gross domestic product (GDP), and E is energy consumption.

Only one plausible solution: zero emissions

For carbon emissions (F) to reach zero, just one of the four terms on the right side of the formula must be zero. So either human population (P), per-person economic activity (G/P), the energy consumed to power the economy (E/G), or the carbon footprint of energy (F/E) must be zero. Common sense gives us the answer to the debate: clean energy is the only plausible route to zero emissions.

And we’re in luck. Clean energy would not destroy humanity or human civilization, which would be the result of zeroing the population, economy, or energy use. Contrary to the false claimsin “Planet of the Humans,” carbon emissions from energy can plausibly reach zero. In fact, a new report from the University of California, Berkeley concludes that U.S. electricity could be supplied by near-zero emissions sources (like wind, solar, hydro, nuclear, and geothermal, plus storage) in short order. About 40% of American electricity is supplied by clean sources as of 2020, and the report concludes that this number could feasibly be scaled up to 55% by 2025, 75% by 2030, 90% by 2035, and 100% by 2045.

If an energy-devouring economy like that of the United States can do it, one might argue, the rest of the world can too.

The Berkeley report also concludes that replacing fossil fuels with clean energy sources would prevent 85,000 premature deaths caused by air pollution and create half a million permanent jobs (mostly associated with manufacturing and construction of clean energy infrastructure), while electricity rates would only be 12% higher than business-as-usual (and cheaper than today’s rates).

A good idea whose time has come?

And this might be the ideal time to accelerate the transition to clean energy. Consider that coronavirus has triggered a recession, cost millions of jobs, and led to the worst health outcomes in areas with high air pollution. Those areas are disproportionately communities of color struggling to achieve racial, environmental, and climate justice.

The report lists numerous policy mechanisms to help achieve this goal – most importantly through clean energy standards that can be set by Congress, governors, state legislatures, public utility commissions, or through an equivalent rulemaking by a new administration’s EPA. Under current business-as-usual policies, just 55% of U.S. electricity will come from clean energy sources in 2035, so accelerating the transition to zero emissions will require implementation of the types of policies outlined in the report.

Electricity accounts for 25% of carbon emissions globally and 28% in the U.S., so achieving net-zero emissions would require additional policies addressing other sectors, for example, electrification of vehicles and building heating sources to power them with clean electricity. Emissions from agriculture, deforestation, and industry processes would also need to be reduced to zero in coming decades. Environmental groups, clean energy advocates, and some political leaders have developed plans and programs that can accomplish all these goals if the public and policymakers get on board.

Why curbing growth isn’t enough

The Gibbs-Moore “Planet of the Humans” film includes interviews with numerous individuals expressing their concerns about human population growth. But the Kaya Identity illustrates why halting or even reversing that growth cannot be the answer to achieving zero emissions. The term “P” is not population growth; rather, it represents the total human population. Zero population would mean human extinction – surely an outcome everyone wants to avoid. Even halving the population like supervillain Thanos in the “Avengers” films – which is not plausible or even desirable – would only halve carbon emissions.

In fact, global population growth has steadily declined from 2% per year in the late-1960s to just over 1% per year today. And most of the growth is happening in developing countries where citizens have small carbon footprints. The climate solutions experts at Project Drawdown note that improving education in developing countries will slow population growth further yet. That will help slow carbon emissions growth, but it cannot achieve the goal of reaching zero emissions.

The second term on the right side of the Kaya Identity, global per capita GDP, has grown at around 2% per year in recent decades, and periods in which it declines represent economic depressions. While curbing excessive consumption in wealthy countries in a shift toward greater sustainability can help slow climate change and other adverse environmental impacts, zero GDP would represent a total collapse of the global economy. Like zero population, it is not achievable if we hope to avoid catastrophe.

Bottom line: Curbing population, economic, and consumption growth can only curb the growth in carbon emissions. Imagine that carbon emissions are the water level in a bathtub that’s filling up. Curbing growth is akin to turning down the water faucet. That’s a start, but not nearly enough to get the water level down to zero; we need to turn off the faucet and unplug the drain.

Clean technologies provide the solutions

The third and fourth terms on the right side of the Kaya Identity represent the energy intensity of the economy (E/G) and the carbon footprint of energy (F/E). The third term has been and is expected to continue declining as energy efficiency improves and as inefficient fossil fuels are replaced by more efficient clean technologies. However, because running the economy will always require energy, this metric also cannot reach zero.

Unlike efforts to curb population and consumption growth, policy solutions that focus on developing and deploying clean technologies can achieve the zero-emissions goal needed in the coming decades to avert a climate crisis. Curbing economic growth can help slow climate change, but only if it doesn’t come at the expense of solutions that can achieve the zero-emissions goal and also benefit communities that have long suffered from racial, environmental, and climate injustices … and whose voices are conspicuously absent from “Planet of the Humans.”

As Mustafa Santiago Ali, vice president for environmental justice at the National Wildlife Federation, told the House Energy and Commerce Committee earlier this month:

People of color are much more likely to live near polluters and breathe polluted air. … We can lessen many of these impacts both in our communities and on our planet by moving forward with a just and equitable transition from fossil fuels, where no one gets left behind and we lower the emissions that are playing a role in COVID-19 impacts and moving us toward a climate emergency tipping point.

Editor’s note: This piece was lightly edited shortly after posting.