Scientists were shocked by how warm it was in 2023. The following year was even hotter

How warm was 2024? By March, just three months into the year, the National Oceanic and Atmospheric Administration had already estimated a 55% chance that 2024 would be the warmest year on record for the planet. By July, they gave it a 77% chance.

It was nearly certain by November.

Turns out, breaking the record was never really in doubt. Last year easily beat out the previous record holder, 2023, for the warmest year on record globally, according to data collected and analyzed by Copernicus Climate Change Service, part of the European Union's climate research program and confirmed by NASA and NOAA scientists.

Copernicus said the global temperature for all of 2024 was 1.6 degrees Celsius above pre-industrial level. NASA's estimate came in slightly lower, with their scientists finding that the earth was 1.47 degrees Celsius warmer than in the mid-19th century. NOAA reported 1.46 degrees Celsius. There is a slight variation in the numbers because each scientific organization conducts its own analysis using different tools. However, the fact that the findings of three independent scientific agencies are so close demonstrates the strength of the data.

It was also a record year for the contiguous United States, according to NOAA. In 2024, the average temperature of the contiguous U.S. was 3.5 degrees Fahrenheit above average and the warmest in its 130-year record.

The year 2024 was the first complete year the planet was warmer than 1.5 degrees Celsius (2.7 degrees Fahrenheit) compared to the pre-industrial average from 1850 to 1900. If that number sounds familiar, it's because the historic Paris Agreement established a 1.5 degrees Celsius warming threshold to prevent the worst impacts of climate change.

Global temperature was above the Paris Agreement threshold for 11 of 12 months, according to Copernicus. We've now had back-to-back record-breaking years for the warmest global temperature and each of the past 10 years has been one of the 10 warmest years on record.

While this is the first calendar year on record to top the 1.5 degrees Celsius warming threshold, it's not the first time the planet has passed that mark, including the 12-month global average temperature between February 2023 and January 2024 and the monthly global average temperature in February 2016.

Exceeding the 1.5 degrees Celsius threshold over several months or even for a few years isn't considered a failure to meet the Paris Agreement's goal. The agreement looks at the global temperature average over multiple decades before making a final determination.

However, climate experts say short-term threshold breaches like we saw in 2024 are an important warning that record-breaking temperatures are likely to continue in upcoming decades if the world doesn't reduce its emissions.

"All of the internationally produced global temperature datasets show that 2024 was the hottest year since records began in 1850. Humanity is in charge of its own destiny but how we respond to the climate challenge should be based on evidence. The future is in our hands -- swift and decisive action can still alter the trajectory of our future climate," said Carlo Buontempo, director of the Copernicus Climate Change Service, in a press statement.

What's causing the warming?

Since last summer, the recent short-term spike in global temperatures has been fueled primarily by the El Ni?o event in the equatorial eastern Pacific. Record highs for global average temperature tend to occur during El Ni?o years.

But an El Ni?o alone isn't causing the record-breaking warming, according to climate scientists. What happened in 2024 is that a short-term El Ni?o spike occurred on top of the gradual, long-term global warming trend primarily driven by human-caused greenhouse gas emissions. Overall, we've seen global warming accelerate during both El Ni?o and non-El Ni?o seasons.

"The defining factor in the evolution of many key climate indicators in 2024 has been the increasing global temperature, which is largely associated with the increasing concentration of greenhouse gases in the atmosphere, a consequence of human activities," said Copernicus.

Copernicus data shows that in 2024, the level of greenhouse gases in the atmosphere reached the highest annual levels ever recorded.

"Our data points clearly to a steady global increase of greenhouse gas emissions and these remain the main agent of climate change," added Laurence Rouil, director of the Copernicus Atmosphere Monitoring Service.

While human-produced greenhouse gas emissions and El Ni?o were key contributors to the 2024 record, some scientists believe there is something else at play as well.

One possibility is that the planet is a victim of its own success in curbing air pollution. In recent decades, regulations, including one in 2020 that drastically cut the amount of sulfur dioxide being released by ships, have significantly reduced the amount of aerosols in the atmosphere.

Aerosols are tiny particles that can reflect sunlight back into space and reduce global temperatures. But their concentrations are now greatly diminished. According to the EPA, U.S. sulfur dioxide emissions have dropped 94% since 1980. The burning of fossil fuels by power plants and other industrial facilities is the largest source of sulfur dioxide in the atmosphere.

While this means cleaner air, fewer atmospheric aerosols also results in a greater amount of sunlight reaching the Earth's surface creating a heating effect. Some research suggests that this may have contributed to recent warm Northern Hemisphere surface temperatures.

Some climate experts believe the January 2022 eruption of the Hunga Tonga-Hunga Ha'apai Volcano may be playing a role in our warming trend. This eruption released an unprecedented amount of water vapor into Earth's atmosphere, according to NASA.

Typically, volcanic eruptions cool the Earth's surface by emitting sulfur dioxide, which transforms into sunlight-reflecting aerosols. However, the 2022 eruption was different, as it released a substantial amount of water vapor—a potent greenhouse gas that traps heat in the atmosphere.

A study published in the American Meteorological Society's Journal of Climate, found that this event could have a significant impact on surface temperatures around the world, triggering warming of over 1.5°C in some regions, while cooling others by around 1°C. However, other studies investigating the eruption have come to very different conclusions.

In July 2024, research published in the Journal of Geophysical Research: Atmosphere concluded that most of the volcano's effects dissipated by the end of 2023. Experts say that the atmospheric aerosol data used in the calculations could be behind the contradicting conclusions.

Copernicus said the total amount of water vapor in the atmosphere hit a record high in 2024.

Climate scientists say one thing is certain. As long as we continue to burn fossil fuels in large amounts, we will continue to see temperatures increasing globally.

To make that point, Andrew Dessler, a professor of atmospheric sciences at Texas A&M shared on social media an email template he reuses each year when reporters ask him about the global temperatures.

His auto reply reads, "No, this is not surprising -- it is exactly in line with predictions. Here is a comment you can use for your story: Every year for the rest of your life will be one of the hottest in the record."

So certain of the trends, Dessler concludes by saying that this year "will end up being among the coldest years of this century. Enjoy it while it lasts."

High hopes with the Paris Agreement

It wasn't supposed to be like this. When the historic Paris Agreement was signed in 2016, then-President Barack Obama said, "Today, the world meets the moment. And if we follow through on the commitments that this agreement embodies, history may well judge it as a turning point for our planet."

But in large part, the world hasn't met the moment nor followed through on its commitments.

In October, the United Nations Environment Programme published a report aptly titled, "No more hot air ... please!" which found the world has made little progress in reversing the use of fossil fuels and faces twice as much warming as agreed to during the Paris Climate Agreement.

The World Meteorological Organization said carbon dioxide concentrations have increased by more than 11% in just two decades, making 2023 a record for the amount of this greenhouse gas currently in our atmosphere.

According to the Global Carbon Project, carbon emissions from fossil fuels hit a record high in 2024 as U.S. crude oil production hit a new record in August 2024, according to the U.S. Energy Information Administration.

So, it was little surprise when researchers at Climate Action Tracker, an independent project tracking government action on climate change, declared that efforts to curb climate change have "flatlined" since 2021.

As leaders fail to take decisive action, the consequences of record-break warming take their toll on lives and property.

Billion-dollar climate consequences

Last year, 27 weather and climate disasters in the U.S. exceeded $1 billion in damage, according to the National Centers for Environmental Information.

These extreme weather events, which ranged from severe storms to hurricanes to wildfires, killed at least 568 people and impacted large swaths of the country.

While climate change may not be responsible for these disasters, human-amplified climate change is making naturally occurring weather events more intense and frequent, according to NASA, NOAA, the United Nations Environment Programme, the Intergovernmental Panel on Climate Change and the U.S. Environmental Protection Agency.

Human-amplified climate change has led to the significant warming of the oceans, which provides the energy hurricanes need to intensify. Hurricanes Beryl and Milton rapidly intensified over unusually warm ocean water, made several hundred times more likely due to human-amplified climate change.

A recent study from Climate Central found that every Atlantic hurricane in 2024 saw an increased maximum wind speed, ranging from 9 to 28 mph, because human-amplified climate change resulted in elevated ocean temperatures. The researchers said it's unlikely Beryl and Milton would have reached Category 5 status without the impact of climate change.

While the severe impact of hurricanes and wildfires is evident in the images of mass destruction, extreme heat is actually the deadliest weather-related hazard in the United States.

Research has discovered that children and adults over 65 are among the most vulnerable to heat-related illnesses and death and the Journal of the American Medical Association found that heat deaths in the United States have nearly doubled since 1999 and represent a 63% increase in death rates caused by heat between 1999-2023.

Extreme heat also affects a child's health, development, behavior, and learning ability. A 2020 study found that a 1°F hotter school year is associated with a 1% reduction in learning that year, based on test scores.

Because our oceans absorb the majority of the planet's heat, global sea temperatures reached record highs for the first half of 2024 and remained well above average for the rest of the year. According to NOAA, this has fueled the largest ocean coral bleaching event on record impacting nearly 77% of coral reef areas.

Uncontrolled climate change is also putting nearly one-third of the world's species at risk for extinction, according to a recent analysis by University of Connecticut researcher and biologist Mark Urban. He found that 160,000 species are already at risk because of changes in our climate.

Reasons to be hopeful

ABC News Chief Meteorologist and Chief Climate Correspondent Ginger Zee said, "1.5 degrees is bad, but it's better than 1.6, which is better than 1.7."

She added, "Each point one degree of warming creates more severe consequences for us, especially the most vulnerable. There's still time to slow or even stop the warming curve if we stop burning fossil fuels and reduce our consumption."

While we haven't reached peak fossil fuel use yet, renewable energy, like wind and solar, is growing exponentially. According to the International Energy Agency (IEA), the "world added 50% more renewable capacity in 2023 than in 2022." The IEA forecasts that the next five years will see the fastest growth yet for clean energy.

Although it was less than many countries wanted, world leaders attending the COP29 UN climate conference agreed to increase contributions to developing nations dealing with the effects of climate change to $300 billion annually by 2035, triple the previous goal of $100 billion.

Companies across the globe are working on ways to collect and store carbon dioxide from the atmosphere and keep it from being released during electricity generation and manufacturing. While these carbon capture and storage technologies are in their infancy and have yet to significantly contribute to reducing our greenhouse gas emissions, billions of dollars are being spent on these efforts.

There are also tens of thousands of green tech companies around the globe working on everything from clean fusion energy to harnessing the power of waves for electricity to making more efficient electric vehicle batteries.