When it comes to concern about global warming, the good news is that a growing number of Americans are alarmed. The bad news is that most still are not alarmed, though they should be given what we already know, how much worse things seem the more we discover and how much we don’t even know we don’t know.

A recent survey by the Yale Program on Climate Change Communication and the George Mason University Center for Climate Change Communication indicates that roughly 60 percent of Americans are either “alarmed” or “concerned” about global warming and that the percentage who are alarmed doubled from 2013 to 2018. The percentage of conservative Republicans who are “very” or “somewhat” worried about global warming more than doubled in the same five-year period, growing from 14 to 32 percent (compared with 80 percent of moderate to conservative Democrats and 95 percent of liberal Democrats as of December 2018).

The percentage of Americans who are “doubtful” or “dismissive” decreased by a combined 11 percentage points in that time, and those who are alarmed now outnumber those who are dismissive three to one (29 percent to 9 percent). The U.S. Department of Defense issued a report in January describing climate change as a national security threat. [AQ: In this sentence, “national security threat” originally had two links in the embedded field, which rendered hyperlinking nonfunctional. Link to the DOD report has been moved. OK?] But more than two in three Americans are still not alarmed—which is alarming.

The U.N. Intergovernmental Panel on Climate Change (IPCC), the leading international body on the assessment of climate change, issued a report in October 2018 indicating that we have already reached 1.0 degree Celsius of global warming beyond preindustrial levels and at current rates are likely to reach 1.5 C between 2030 and 2052, at which point there will be an increased risk of extreme weather events such as droughts and floods; higher sea levels threatening the lives of millions of people; greater species loss and extinction; and growing risk to water supplies, food security, economic growth, and human health and safety. Some impacts may be irreversible.

What we already know underscores the need for urgent action. The IPCC report indicates the need to cut carbon dioxide [AQ: “greenhouse gas” changed to “carbon dioxide” because the report refers to CO 2 emissions specifically in relation to this value; numbers for other greenhouse gases such as methane are different.] emissions by approximately 45 percent by 2030, relative to 2010 levels. [AQ: In the model mentioned here, carbon dioxide emissions also reach net zero around 2050. Is this an essential part of the calculation—that is, would it be misleading to mention reductions by 2030 in isolation as the recommended course of action?] Debra Roberts, cochair of an IPCC working group, said of the report, “It’s a line in the sand and what it says to our species is that this is the moment and we must act now.”

Recent scientific discoveries further underline the need for prompt and effective action. According to a study published in Science last week, [AQ: Do you want to link directly to the Science paper here? https://doi.org/10.1126/science.aax3528 ] scientists using a new method of measuring the rate at which glaciers melt below the surface of the water concluded they are melting 10 to 100 times faster than previously thought. That means that sea level rise and carbon release from melting glaciers are also occurring faster than scientists realized, with unknown consequences for the whole food web.

The tiny marine organism Prochlorococcus provides a cautionary tale about what we might not even know we don’t know. A Smithsonian article explains that most of the oxygen we breathe comes from organisms in the ocean that release oxygen into the atmosphere while making food for themselves through the process of photosynthesis.

Prochlorococcus, the most abundant of these photosynthesizers, is so small that millions can fit in a drop of water. It produces approximately 20 percent of the oxygen we breathe. [AQ: Links under “millions can fit” and “approximately 20 percent” are identical. OK? ] But scientists didn’t even know it existed until 1988, just over 30 years ago.

That should make us wonder what other “unknown unknowns” might be vital to our long-term survival.

We also still don’t know enough about how complex phenomena related to global warming are interrelated. A recent study by the Harvard T. H. Chan School of Public Health shows that in addition to warming the planet, rising carbon dioxide levels also reduce the levels of vitamins and other nutrients in edible plants, including in grains such as rice, on which the nutritional well-being of millions of people depends. Health impacts may include neural-tube defects in unborn children, beriberi, skin lesions, nervous disorders, migraines, and loss of appetite in adults.

This month, scientists in Iceland will commemorate [Note to editor: the ceremony will take place on August 18, so “will commemorate” should be changed if the piece is published later than that.] that country’s first lost glacier with a plaque containing “a letter to the future” on which is written, “This monument is to acknowledge that we know what is happening and what needs to be done. Only you know if we did it.”

Hopefully more of us will become alarmed enough to do what needs to be done and to earn the gratitude rather than the scorn of future generations.