Enlarge (credit: US EIA )

On Thursday, the US Department of Energy released its preliminary estimate for the nation's carbon emissions in the previous year. Any drop in emissions puts us on a path that would avoid some of the catastrophic warming scenarios that were still on the table at the turn of the century. But if we're to have a chance of meeting the Paris Agreement goal of keeping the planet from warming beyond 2° C, we'll need to see emissions drop dramatically in the near future.

So, how is the US doing? Emissions continue to trend downward, but there's no sign the drop has accelerated. And most of the drop has come from a single sector: changes in the power grid.

Off the grid, on the road

US carbon emissions have been trending downward since roughly 2007, when they peaked at about six gigatonnes. In recent years, the pandemic produced a dramatic drop in emissions in 2020, lowering them to under five gigatonnes for the first time since before 1990, when the EIA's data started. Carbon dioxide release went up a bit afterward, with 2023 marking the first post-pandemic decline, with emissions again clearly below five gigatonnes.

Enlarge (credit: Jose A. Bernat Bacete )

Today, the US Environmental Protection Agency announced a suite of rules that target pollution from fossil fuel power plants. In addition to limits on carbon emissions and a tightening of existing regulations on mercury releases, additional rules target coal ash waste left over from power generation and contaminants in the water used during the operation of power plants. While some of these regulations will affect the operation of plants powered by natural gas, most directly target the use of coal and will likely be the final nail in the coffin for the already dying industry.

The decision to release all four rules at the same time goes beyond simply getting the pain over with at once. Rules governing carbon emissions are expected to influence the emissions of other pollutants like mercury, and vice versa. As a result, the EPA expects that creating a single plan for compliance with all the rules will be more cost-effective.

Targeting carbon

The regulations that target carbon dioxide emissions have been in the works for roughly a year. The rules came in response to a Supreme Court decision in West Virginia v. EPA , which ruled that Clean Air Act regulations had to target individual power plants rather than giving states flexibility regarding how to meet broader standards. As a result, the new rules target carbon dioxide the only way they can: Plants can either switch to burning non-fossil fuels such as green hydrogen, or they can capture their carbon emissions.

Enlarge / Sultan Ahmed Al Jaber defied expectations to deliver a document that explicitly calls for limits on fossil fuel use. (credit: Fadel Dawod )

On Wednesday, the UN's COP28 meeting wrapped up with a major success: Despite a bruising fight with OPEC nations , the closing agreement included a call for a transition away from fossil fuels. There's still plenty here for various parties to dislike, but this is the first agreement that makes the implications of the Paris Treaty explicit: We can't limit climate change and continue to burn fossil fuels at anything close to the rate we currently do.

Beyond that, however, the report has something to disappoint everyone. It catalogs strong signs of incremental progress toward the Paris goals while acknowledging we're running out of time for further increments. And the steps it calls for will likely keep changes on a similar trajectory.

Taking stock

The new document is called a "Global Stocktake" in reference to checking the world's progress toward the goals of the Paris Agreement: limit climate change to 2° C above preindustrial temperatures and try to keep it to 1.5° C. That agreement called for nations to make pledges to limit greenhouse gas emissions; initial pledges were insufficient, but regular meetings of the Conference of the Parties (COP) would allow the pledges to be updated, raising their aggressiveness until the world is on a trajectory toward meeting its goals.

Enlarge / Saudi Arabia's presence at COP28 has reportedly been used to limit progress on fossil fuel cutbacks. (credit: Sean Gallup / Getty Images )

Oil-producing countries are apparently succeeding in their attempts to eliminate language from an international climate agreement that calls for countries to phase out the use of fossil fuels. Draft forms of the agreement had included text that called upon the countries that are part of the Paris Agreement to work toward "an orderly and just phase out of fossil fuels." Reports now indicate that this text has gone missing from the latest versions of the draft.

The agreement is being negotiated at the United Nations' COP28 climate change conference , taking place in the United Arab Emirates. The COP, or Conference of the Parties, meetings are annual events that attempt to bring together UN members to discuss ways to deal with climate change. They were central to the negotiations that brought about the Paris Agreement, which calls for participants to develop plans that should bring the world to net-zero emissions by the middle of the century.

Initial plans submitted by countries would lower the world's greenhouse gas emissions, but not by nearly enough to reach net zero. However, the agreement included mechanisms by which countries would continue to evaluate their progress and submit more stringent goals. So, additional COP meetings have included what's termed a "stocktake" to evaluate where countries stand, and statements are issued to encourage and direct future actions.

Enlarge / The facility seen in this architect's rendering will not be built. (credit: Idaho National Lab )

Nuclear power provides energy that is largely free of carbon emissions and can play a significant role in helping deal with climate change. But in most industrialized countries, the construction of nuclear plants tends to grossly exceed their budgeted cost and run years over schedule.

One hope for changing that has been the use of small, modular nuclear reactors, which can be built in a centralized production facility and then shipped to the site of their installation. But on Wednesday, the company and utility planning to build the first small, modular nuclear plant in the US announced it was canceling the project.

Going small

Small modular reactors take several steps to potentially cut costs. Their smaller size makes it easier for passive cooling systems to take over in the case of power losses (some designs simply keep their reactors in a pond). It also allows the primary components to be built at a central facility and then shipped to different plant sites, allowing a lot of the manufacturing equipment to be reused for all the sites that use the reactors.

Enlarge / Natural gas plants like these may find themselves burning hydrogen over the next 20 years. (credit: Ron and Patty Thomas )

Today, the Biden administration formally announced its planned rules for limiting carbon emissions from the electrical grid. The rules will largely take effect in the 2030s and apply to gas- and coal-fired generating plants. Should the new plan go into effect, the operators of those plants will either need to capture carbon or replace a large fraction of their fuel with hydrogen. The rules will likely hasten coal's disappearance from the US grid and start pushing natural gas turbines to a supplemental source of power.

Whether they go into effect will largely depend on legal maneuvering and the results of future elections. But first, the rules themselves.

Clearing the air

Back in 2007, the US Supreme Court ruled that the Clean Air Act applied to greenhouse gas emissions . This allows the EPA to set state-level standards to limit the release of greenhouse gasses, with the states given some leeway on how they reach those standards. Since then, the court has clarified that these standards must be met on a per-plant basis rather than at the grid level; the EPA can't set rules that assume that the grid has more generation from solar and less from coal plants.

Enlarge / The next generation of reactors may be small and modular and use different coolants. (credit: Getty Images )

"The race against climate change is both a marathon and a sprint," declares a new report from the US National Academies of Science . While we have to start decarbonizing immediately with the tech we have now—the sprint—the process will go on for decades, during which technology that's still in development could potentially play a critical role.

The technology at issue in the report is a new generation of nuclear reactors based on different technology; they're smaller and easier to build, and they could potentially use different coolants. The next generation of designs is intended to avoid the delays and cost overruns that are crippling attempts to build additional reactors both here and overseas. But their performance in the real world will remain an unknown until next decade at the earliest, placing them squarely in the "marathon" portion of the race.

The new report focuses on what the US should do to ensure that the new generation of designs has a chance to be evaluated on its merits.

Enlarge / A German nuclear power plant, which is currently partially closed. (credit: Getty Images )

In 2011, in the wake of the Fukushima disaster, Germany decided to shut down all of its nuclear power. The process was supposed to have ended last year, but it has been extended in response to energy uncertainties caused by the war in Ukraine. As a result, even though renewable generation in Germany continues to climb, the country's carbon emissions have only trended down slowly.

While there's no indication that the US will follow Germany down this path—the Biden administration is actively subsidizing nuclear plants to keep them open—the economics of nuclear power have led to a number of plant shutdowns. It's currently the second-most expensive major source of power, just ahead of offshore wind, with the costs of wind continuing to drop. So there's a significant chance that nuclear's contribution to the US grid will shrink.

A new analysis shows that a drop in nuclear power on the current US grid will mean enough additional pollution to cause over 5,000 deaths each year, and the burden of those deaths will fall disproportionately on Black Americans. But on a future grid where renewables are present at sufficient levels to offset the loss of nuclear, almost all of these additional deaths can be avoided.

Enlarge (credit: MOF )

Currently, the major oil companies appear to have settled on an awkward compromise with the reality of climate change: They generally acknowledge that their product is helping drive it but plan to continue to produce as much of that product as they can. But that reflects a major change for these companies, which up until recently were funding think tanks that minimized the risks of climate change and, in many cases, directly denying the validity of the science.

In the case of ExxonMobil, that includes denying its own science. Thanks to documents obtained by the press, we now know that Exxon sponsored its own climate researchers who did internal research, collaborated with academic scientists, and came to roughly the same conclusions about carbon dioxide that the rest of the scientific community had—and executives were made aware of it.

But how rough were the conclusions that Exxon's scientists gave its executives? It's a question that goes to the heart of how misleading the executives were being when they downplayed the risks. A new study answers that question pretty definitively: Exxon's scientists were as good (and sometimes better) than the scientific community as a whole at projecting the climate changes created by fossil fuel use.