BERLIN (AP) — This year's U.N. climate summit renews an urgent question to the international community: Can the world come together to confront the common enemy of global warming before it's too late?

The talks that start Sunday in Scotland were always bound to be tense, but the coronavirus pandemic, the ensuing economic crisis and the recent energy crunch have put even more pressure on the two-week meeting.

Here are five of the top issues that will need to be tackled in Glasgow:

RICH COUNTRIES OWE POOR ONES

The pledge by rich countries to mobilize $100 billion each year for poor nations to cope with climate change was likely missed in 2020. Estimates for 2019 show the funding was just shy of $80 billion.

The failure to deliver on a promise first made in 2009 has caused deep anger and distrust among poor nations, with some threatening to block any agreement until the money is provided.

There is no set formula for how much each country should contribute toward the total, or how. But the Washington-based World Resources Institute calculated that only a handful of rich countries, including France, Japan, Norway, Germany and Sweden, provided a fair share. The United States, Australia and Canada fell far short.

One solution proposed this week is for the payments to average $100 billion per year from 2021 to 2025, with the shortfall in earlier years made up for by higher payments later on.

Developing countries will use the Glasgow talks to press for half the money to be earmarked for projects aimed at adapting to climate change. At the moment, most of the funding goes toward reducing emissions.

Poor nations also insist it's also time to address who will pay for the damage to habitats and livelihoods from rising seas, growing deserts and more extreme weather.

“Our people are suffering in a variety of ways as a result of a crisis that they did little to cause," said Sonam P. Wangdi of Bhutan, who chairs the Least Developed Countries group at the talks.

CARBON TRADING

Some unfinished business from the Paris climate summit in 2015 involves the rules for international carbon trading, which is seen as a key instrument to harness market forces in the fight against global warming.

Negotiators failed to finalize this part of the Paris rulebook in Madrid two years ago. They will make another attempt in Glasgow. On one side will be countries that want tighter rules to avoid worthless carbon vouchers flooding the market. On the other side will be developing nations that insist certificates amassed under previous agreements should be honored.

The rules are critical because for many countries and companies to achieve “net zero” emissions by midcentury, pollution will have to be balanced out by an equal amount of carbon reliably captured elsewhere, such as through forests or technological means.

Establishing a truly international carbon market also presents an opportunity to raise money through transaction fees, but who manages those and how remains unresolved.

ENSURING TRANSPARENCY, COMMITTING TO NEW TARGETS

Transparency is a key element of the talks, because the voluntary nature of the Paris accord means countries closely watch what how much progress others make before ratcheting up their targets another notch.

Another debate centers around the time frame for reporting fresh pollution-reduction targets. Current agreements require developed countries to set new goals every five years, but some participants want to shift to annual pledges, at least until the world is on track to meet the Paris goals.

METHANE

Methane, the main component in natural gas and a byproduct of some agriculture, has been somewhat overlooked in past negotiations.

As a greenhouse gas, it's about 20 times more potent than carbon dioxide but stays in the air for only about a decade. Reducing emissions by fixing leaks in gas pipelines and limiting flaring at drilling sites would provide a small but noticeable improvement.

The world cannot solve the climate problem without cutting methane, said Kelly Levin, chief of science, data and systems change at the Bezos Earth Fund.

THE 45% PLEDGE

A proposed pledge to reduce emissions by 45% by 2030 compared with 2010 levels is not so much a negotiating point as a goal established by the U.N. for the talks to be considered a success. So far, emissions are going up, not down.

Halving emissions in the next decade is considered a key stepping stone on the path to net zero by 2050, which scientists say is the only way to achieve the Paris accord's goal of capping global warming at 1.5 Celsius (2.7 Fahrenheit) by the end of the century.

Borenstein reported from Washington.

Follow AP's coverage of the climate talks at http://apnews.com/hub/climate