Swedish climate activist Greta Thunberg on Wednesday denounced the pledges of wealthy countries and businesses to curb climate change as hollow and deceptive, calling them "clever accounting and creative PR" in a speech before world leaders at the United Nations' annual COP25 climate meeting in Madrid.

The talks are aimed at finalizing guidelines for implementing the 2015 Paris Agreement, which called for measures to prevent global temperatures from rising more than 3.6 degrees Fahrenheit and mitigate the consequences of climate change.

Thunberg, addressing the conference hours before she was named Time magazine's Person of the Year for 2019, criticized the targets for reducing greenhouse gas emissions and declarations of climate emergencies for falling short of real, substantial action.

"This is not leading. This is misleading," Thunberg, 16, said. "Only setting up distant dates and saying things which give the impression that action is underway will most likely do more harm than good."

A 2018 Intergovernmental Panel on Climate Change report warned that to evade the most serious consequences of climate change by keeping global temperatures from rising more than 2.7 degrees, emissions would have to be reduced significantly by 2030.

Swedish climate activist Greta Thunberg gives a speech during a high-level event on climate emergency hosted by the Chilean presidency during the UN Climate Change Conference COP25 in Madrid, on Dec. 11, 2019. Cristina Quicler / AFP - Getty Images

The effects of climate change are becoming ever more apparent.

The U.S. National Oceanic and Atmospheric Administration released a report on the state of the Arctic on Tuesday that found air temperatures were the second warmest since 1900, contributing to record losses to the Greenland ice sheet and exceptional snow melt in the Canadian Arctic and Alaska.

The melting ice also means permafrost ecosystems could release up to 600 million tons of carbon dioxide per year, contributing to further global warming.

In the wake of calls for action on climate change, many governments have declared climate emergencies and set more stringent targets — including the European Union, which plans to reduce carbon emissions by 50 percent by 2030. As leaders negotiate how to achieve such targets and who should pay for it, Thunberg said the effort is misleading as global emissions hit record highs.

"Most of these pledges do not include aviation, shipping, importing and exporting goods and consumption, but they do include the possibility for countries to offset their emissions elsewhere," she said. "Without seeing the full picture, we will not solve this crisis."

The shortcomings of world leaders and the inequality at the heart of the climate crisis which is "created by rich countries," was also addressed by Ugandan youth activist Hilda Flavia Nakabuye.

"You have been negotiating for the last 25 years, even before I was born," she said. "Do you want the whole of Africa to perish?"

Following her appeal, a group of youth activists staged a sit-in protest at the climate talks, which is set to lose a key signatory. President Donald Trump last month wrote a letter to the U.N. to start the withdrawal process from the international climate pact.

Michael Bloomberg, the New York billionaire and presidential candidate, reassured climate activists in Madrid this week that Americans remain committed to reducing greenhouse gas emissions "even with a climate change-denier in the White House," promoting efforts by U.S. states, cities and businesses to continue to abide by the Paris accord.