In the blitz of media coverage following the Trump administration's Black Friday release of the Fourth National Climate Assessment (NCA4), one statistic kept popping up:

By the end of the century, global warming could cost the U.S. 10% of its gross domestic product.

I spent part of this week tracking down the origins of that frightening statistic.

Why it matters: This figure has been used to indicate that global warming will inflict massive economic costs on the U.S. if dramatic actions to adapt to climate change and curtail emissions are not taken in the next decade.

• Critics, including the White House, have seized upon the statistic to paint the report as "radical" and "extreme."
• The White House and EPA are attacking the figure and say billionaire activists and research funders Tom Steyer and Michael Bloomberg are behind it.

Background: The stat can be traced to a 2017 study, published in the journal Science, that quantified the economic costs to the U.S. for various amounts of climate change.

Amir Jina, an economist at the University of Chicago and a co-author of that study, told Axios he was not surprised the 10% statistic was used in the NCA4, but he has been "a little disappointed" at how the media focused on it.

"I still obviously stand by the work that we did, and that number does come from this paper, but I think it needs more nuance in the way that it’s presented,” Jina told Axios.

Details: The study, based on a meta-analysis of the peer reviewed literature as well as extensive new modeling, projects that nationwide, for every 1°C increase in average temperature, U.S. GDP will drop by 1.2%.

• If anything, the GDP figures in the study could be an underestimate, Jina said. It only accounted for sectors that are well-researched and measured, not for the whole economy.
• The 10% figure does in fact derive from an extreme warming scenario, one in which the climate warms by about 8°C, or 14.4°F, by 2100. That is within the realm of possibility.
• But the average finding for a high-emissions scenario would amount to a mean warming of about 4–4.5°C, or 8.1 °F, compared to preindustrial levels.
• The GDP losses from that range of warming is still "large and shocking and terrible," said Jina.

Funding: Jina, and lead author Solomon Hsiang of U.C. Berkeley, told Axios the 2017 study moved the science well beyond findings of earlier work Steyer and Bloomberg funded and mainly relied on other sources.

Hsiang also said the funders had no input on the study's conclusions.

It's not an outlier: Michael Oppenheimer, a geosciences researcher at Princeton and study co-author, told Axios that the cost estimates included in the NCA4 would be similar even if this study was not in it, given other work on the topic.

Go deeper:

• Where climate change will hit the U.S. hardest
• New climate report warns of increasingly dire risks to U.S.
• White House criticizes its climate report as "not based on facts"

China is temporarily suspending the work of scientists who claimed twins were born after being genetically edited as embryos.

Why it matters: The scientific consensus is that gene editing embryos at this stage of science is "irresponsible." But, while this particular experiment has not been verified, the fact is the technology is available to researchers, so there's a growing call for international limitations on its use.

ICYMI: Chinese scientist He Jiankui announced earlier this week that twins were born after he used the gene-editing tool CRISPR-Cas9 to cut the CCR5 gene that's known to play a role in HIV infection.

• He stirred even more dismay when he mentioned the possibility of a second pregnancy.
• China currently bans human implantation of gene-edited embryos. Its Ministry of Science and Technology is investigating the claims, per Xinhua.

There are concerns about the safety, efficacy and possible mosaicism, where a person can contain genes in both its edited and unedited forms, from cutting genes.

• Editing embryos raises an even bigger concern: The genetic changes and all the unknowns around them can be passed down to future generations.

Between the lines: Not everyone viewed it as a complete disaster. For instance, Harvard Medical School's George Daley suggested that it may be time to reconsider the massive amounts of research done over the past several years and look for plausible methods of moving forward.

What to watch: Scientists are cautious about predicting what the impact will be, in part because the details of this claim are thin. However, the debate is heating up and one concern is it will dampen important research.

• Medical ethicist Jonathan Moreno from the University of Pennsylvania says the situation reminds him of other times in history where there were tremors in the science world, like the death of 18-year-old Jesse Gelsinger in 1999 from a gene therapy trial that led to years of diminished research.

The bottom line: The alarm over what could be next is real. But scientists hope the current debate will promote consensus on firm limits and promote transparency.

Go deeper:

• The ethical red flags of genetically edited babies
• Controversial Chinese scientist hints at another gene-edited pregnancy
• CRISPR co-inventors warn about editing embryos

One of the key questions addressed in the Fourth National Climate Assessment is one of timing: When will the U.S. begin to feel the impacts of global warming?

The answer is unsettling, because it's past tense.

• We've been seeing the impacts, in the form of hotter and longer-lasting heat waves as well as sea-level rise and more frequent coastal flooding, for years.

Why it matters: We're not responding in the ways climate experts hope we will, at least not yet.

“This is a risk management problem par excellence," said Princeton's Oppenheimer. "We would have to be incredibly irresponsible” not to take action in light of what is known about climate change, he said, speaking of both adaptation to climate impacts today and emissions cuts.

The trends: According to a new report from Climate Central and the real estate data firm Zillow, in more than 50% of coastal states, homes are being built at a faster rate in areas at risk of flooding from sea-level rise than the rate of new homes in safer areas.

• Overall, they say about 386,000 current coastal U.S. homes are expected to be at risk of regular flooding by 2050, because of rising seas caused mainly by climate change.
• With increased sea-level rise through the year 2100, 2.5 million homes — worth $1.3 trillion — would be subjected to regular flooding if emissions continue to increase unchecked.
• Harris County, Texas, home to Houston, is building homes in flood-prone areas at 1.4 times the rate that it is building homes in non-flood-prone areas.
• On the other hand, Brunswick County, North Carolina, is building homes in flood-prone areas at 1/5th the rate as in non-flood-prone areas.

"It’s difficult to plan for higher seas if you are busy digging deeper holes," said Benjamin Strauss, CEO and chief scientist of Climate Central, in a press release.

Life expectancy: Spurred by a spike in suicide, overdose deaths and hunger, life expectancy in the U.S. has been declining for the past three years.

Global goals: The UN's goal of ending global hunger by 2030 is slipping out of reach due to conflict, climate change and other factors.

Mars lander: NASA's Mars InSight lander became the first spacecraft to successfully land on Mars since 2012 when it touched down on Nov. 27. It's mission: to drill deep into Mars' interior and explore how the planet formed.

The insect apocalypse: Brooke Jarvis writes for the New York Times Magazine about the global decline in insects and what it might mean for human culture, natural systems and survival.

Open water: The Inuit are seeking more control over a vast opening in the sea ice between Greenland and Canada’s Ellesmere Island that typically forms each year, writes Julia Rosen for Hakai Magazine.

Moon landers: NASA is partnering with 9 companies to send small robotic landers to the moon, the agency announced today. The landers are "a first phase in a multiyear plan to put humans on the lunar surface again," reports Loren Grush for The Verge.

Blue whales are changing their tune, according to a new study published in the Journal of Geophysical Research: Oceans.

Why it matters: The global decline in the pitch of whale songs has been a mystery, with chief suspects being the increase in ocean noise from shipping, submarines and underwater resource exploration. The new study, however, suggests other factors may be behind the trend.

Details: The researchers found that a seasonal variation to Antarctic blue whales' pitch correlates with breaking sea ice in the southern Indian Ocean, suggesting that seasonally they're laboring to make their voices heard above the crackling and grinding sounds of breaking ice.

• Only male blue whales sing, and their hums can be about as loud as large ships.
• A single blue whale's sounds can travel for 600 miles underwater, enabling whales to communicate with one another across long distances.

What they did: The paper analyzed more than 1 million songs from three species of large baleen whales: fin, Antarctic blue and three acoustically distinct populations of pygmy blue whales.

• Six stationary underwater microphones recorded the calls over 6 years, from 2010 to 2015, in the southern Indian Ocean, an area spanning 3.5 million square miles.
• The study's authors analyzed the pitch of selected elements of each species’ song.

What they found: Between 2002 and 2015, the pitch of blue whales' calls had fallen by "about a whole tone or major second interval in Western music tradition," the press release states.

This trend is intriguing, but has not yet had major consequences.

• The fact that the pitch drop was observed in the southern Indian Ocean, where ship noise has decreased in recent years, suggests an uptick in global ocean noise is not the cause of the downward trend in whale pitches.
• Instead, increasing blue whale populations could be resulting in a natural shift in volume, since whales may not need to sing as loudly to reach another whale.

“They can decrease their call intensity to keep in touch, because there are more whales," Emmanuelle Leroy, lead author of the new study and a research fellow at the University of New South Wales in Australia, said in a press release. "These calls are long distance communication.”