Many large countries with commitments to reach net-zero emissions around mid-century - particularly major oil and gas-producing nations - say they intend to achieve net-zero in part by using "carbon capture and storage" (CCS).
The technology involves capturing planet-heating gas emitted from fossil fuel power stations, industrial plants and similar sources and then pumping it into permanent storage underground.
But critics say national net-zero plans foresee dramatically more use of CCS than is actually being developed, and that the expensive technology is simply not capable of capturing enough emissions to keep fossil fuels viable and the planet safe.
The oil and gas industry should be "letting go of the illusion that implausibly large amounts of carbon capture are the solution," warned Fatih Birol, executive director of the International Energy Agency (IEA), ahead of COP28.
Here's why CCS is popular, but controversial:
WHY IS THIS A BIG ISSUE AT COP28?
Fossil fuel-producing nations are under unprecedented pressure at COP28 to agree, for the first time, to "phase out" the use of fossil fuels as the basis of global energy systems.
That is because still-rising fossil fuel emissions are rapidly heating the planet and driving more costly and dangerous extreme weather, such as hurricanes, droughts, floods and wildfires, as well as other impacts like rising sea level.
With the world now expected by 2027 to at least temporarily hit the warming limit of 1.5 degrees Celsius set in the Paris Agreement, with the risk of triggering catastrophic global 'tipping points' - scientists say fossil fuels need to be swiftly phased out in favour of renewable energy sources.
"1.5C is not a target, it is not a goal, it is a physical limit," warned Johan Rockström, director of the Potsdam Institute for Climate Impact Research, speaking to reporters at COP28.
But many oil and gas-producing states say the focus instead should be on using technology such as CCS to eliminate climate-changing emissions, not necessarily fossil fuels themselves.
COULD FOCUSING JUST ON EMISSIONS WORK?
Investment is fast rising in carbon capture - both to tackle emissions from power and industrial plants, and eventually aimed at sucking large volumes of carbon dioxide back out of the air to push temperatures back down below the 1.5C warming limit.
Around the world about 41 projects are now operating and more than 350 are in development, according to the Global CCS Institute, a think-tank.
The United States, Britain, Canada, China and Norway are among the leaders in pushing ahead projects, the institute noted.
But, even as it increases, that investment is "well below what is required" to meet existing net-zero emissions commitments, the IEA noted ahead of COP28.
As well, CCS technology does not capture all of the emissions from power plants or industrial facilities.
At least 10% of the emissions from coal plants - the most polluting fossil fuel plants - still escape when CCS is in use, said Oliver Geden, a carbon dioxide removal expert at the German Institute for International and Security Affairs.
A push at COP28 to allow continued use of "abated" fossil fuels - such as those used with CCS technology - could result in large amounts of carbon emissions still reaching the atmosphere, particularly if what constitutes an "abated" fuel remains poorly defined.
With emissions reductions from a fossil fuel source of as low as 51% potentially qualifying as abated, "CCS is a lifeline for the fossil fuel industry, not people and planet," warned advocacy group Oil Change International.
"CCS has a 50-year track record of over-promising and under-delivering, and every investment in CCS provides a lifeline to the fossil fuel industry," the group noted in a statement at COP28.
IS THE INTENDED USE OF CCS TECHNOLOGY TO KEEP FOSSIL FUELS GOING?
Climate scientists say use of carbon capture and storage technology is now unavoidable to try to deal with an expected overshoot of the 1.5C temperature goal.
But such technology should be used mainly to capture emissions from industries that are, for now, particularly hard to run on renewables - such as steel or cement-making, scientists say.
They say the world's limited underground carbon storage reservoirs also should be held in reserve to handle the carbon dioxide that will eventually need to be sucked from the air.
That will likely be done using so-called "direct air capture" machines - a for-now hugely expensive technology but one with potential to reverse dangerous temperature overshoots.
Growing trees or other vegetation that absorb carbon dioxide and then harvesting and burning that "biomass" in power plants, with the emissions captured and stored underground, could be another means of creating the "negative emissions" that will be needed, scientists say.
But with the world already perilously close to passing the 1.5C mark, CCS and other carbon removal technologies "cannot be used as an excuse to keep expanding coal, oil and gas production and use", Ploy Achakulwisut, a research fellow in Bangkok for the Stockholm Environment Institute, warned at COP28.
The cost of using CCS in a bid to keep fossil fuels viable is another concern.
Researched released by the Oxford Smith School of Enterprise and the Environment at the U.N. summit found that using limited CCS but more renewables to reach net-zero by 2050 would cost $1 trillion less a year than using more fossil fuels and more CCS.
IS CCS BEING PROMOTED AS A WAY TO GREENWASH FOSSIL FUELS?
Countries with economies built on oil production and exports are reluctant to give up their huge profits, which in 2022 hit more than $200 billion, a doubling from the previous year.
Swiftly transitioning economies away from climate-damaging fossil fuels also is challenging, costly and requires lifestyle changes not all want to make.
But Nikki Reisch, climate and energy programme director for the U.S.-based Center for International Environmental Law, said the push by oil and gas-producing states for "abated" fossil fuel use amounts to "nothing more than greenwashing".
"No amount of carbon capture or offsets can make fossil fuels climate-friendly," she insisted.
Former Irish President Mary Robinson, now a climate justice advocate, similarly called abated fossil fuels "a false solution" that would "provide a loophole for emitters to continue".
"Relying on these hypothetical solutions is something like bailing out with a bucket instead of plugging the hole," Robinson, now chair of The Elders, a group of leaders working on peace, justice and sustainability issues, told Context.
"We must deal with what is harming us - and that is fossil fuel," she said.
Even Birol, the IEA chief, has warned that "the oil and gas industry is facing a moment of truth at COP28 in Dubai."
"With the world suffering the impacts of a worsening climate crisis, continuing with business as usual is neither socially nor environmentally responsible," he noted.
