ILLUSTRATION: C. BICKEL/SCIENCE802 12 NOVEMBER 2021 • VOL 374 ISSUE 6569
I
n 2000, the U.S. astronomy “decadal
survey”—a prioritized wish list that
guides Congress and funding agencies—
said its top priority was the giant, infra-
red James Webb Space Telescope. Two
decades later, astronomers have again
put a giant space telescope at the top of
their 10-year list. But this time, they hope it
will be the first in a series of space observa-
tories working across different wavelengths,
from x-rays to the far infrared—“a fleet, not
just the flagship,” says John O’Meara, chief
scientist of the W. M. Keck Observatory.
The Webb telescope, which should finally
launch next month (see p. 806), ended up
wildly delayed and overbudget, with a cost
that has reached $10 billion. It is sometimes
called the “telescope that ate astronomy.” In
the latest survey, released last week, a panel
of astronomers kept ambitions for their
next great telescope in check. No bigger or
costlier than Webb, but sensitive to opti-
cal wavelengths so it can search for life on
nearby Earth-like exoplanets, it is meant to
allow room for other orbiting observatories,
reminiscent of the complementary Hubble,
Spitzer, Chandra, and Compton space tele-
scopes in the 1990s and 2000s. “It’s a ratio-
nal, balanced plan,” says astronomer Wendy
Freedman of the University of Chicago.
The survey ranks ground-based facilities
with an equally pragmatic eye. It recom-
mends the National Science Foundation
(NSF) buy a stake in two enormous opti-
cal telescopes that are already in develop-ment—the Giant Magellan Telescope (GMT)
and the Thirty Meter Telescope (TMT). “It’s
hard to imagine the scientific community
not having access to large telescopes in
the coming decades,” says survey co-chair
Fiona Harrison of the California Institute of
Technology.
The report also calls for boosting NSF’s
grant program, supporting early-career sci-
entists, and providing a bigger budget for
operating existing facilities. And it chides
universities and funding agencies over their
records on diversity and openness to under-
represented groups (see sidebar, p. 803).
“There’s a lot of talent that is untapped and
people who don’t feel they have a place in
astronomy,” O’Meara says. “The committee
has charged us with change.”
To produce the report, Harrison and co-
chair Robert Kennicutt of the University of Ar-
izona led a 20-person steering committee that
weighed recommendations from 140 other
astronomers in 13 subpanels. Other input
came from hundreds of submitted white pa-
pers and numerous town hall meetings. The
strictures of the COVID-19 pandemic meant
almost all deliberations were done virtually,
which added a year to the process.
NASA had commissioned studies of four
potential cornerstone missions in advance,
to give the committee a better sense of their
capabilities and costs (Science, 14 December
2018, p. 1230). These included a large general
purpose optical observatory with a mirror
up to 15 meters across, a smaller optical tele-Zeke Hausfather, a climate scientist at the
Breakthrough Institute, an environmental
research center. A U.N. report released in
October found pledges made to that point
would keep warming to about 2°C, whereas
a similar International Energy Agency
(IEA) analysis projected 2.1°C. So, it’s “not
very surprising” that new pledges trimmed
a few more tenths, Hausfather says.
Shortly before the summit, Meinshausen
and his colleagues compiled the pledges
that nations had submitted to the United
Nations, including both near-term prom-
ises to reduce emissions by 2030 and longer
term pledges to reach net zero emissions by
2050 to 2070. Some pledges depend on na-
tions receiving financial support, whereas
others are unconditional. The researchers
fed the promised emissions levels into a
climate simulation that generated a range
of possible warming outcomes.
The presummit pledges would lead to
between 1.5°C and 3.2°C of warming this
century, the projections showed, with a
50% chance of staying below 2.1°C. But the
new commitments offer a 50% chance of
staying below 1.9°C. (The range of possible
warming is 1.3°C to 2.7°C.)
In the second analysis, released on 4 No-
vember, IEA found that if all current com-
mitments “are met in full and on time,”
warming could be limited to 1.8°C by 2100.
Joeri Rogelj, a climate scientist at Impe-
rial College London, cautions that even if
nations meet their pledges perfectly, there
is still a 50% chance of exceeding the 2°C
target. He also notes that high-level an-
nouncements made at the summit lack
crucial detail. India, for example, didn’t
say whether its commitment to net zero
emissions by 2070 applies only to carbon
dioxide or to all greenhouse gases.
There’s a risk that politicians will use the
new projections to justify inaction, Rogelj
says. For example, many nations, such as
Australia, are still expanding their use of
fossil fuels while declaring ambitious cli-
mate goals. “There is very low confidence,
with the evidence that we have, that those
pledges will be implemented,” Rogelj says.
Meinshausen adds that developing coun-
tries will need financial help from wealthy
nations to realize their pledges. “It’s not
only whether we believe [the pledges],” he
says, “but also a question of support.”
Keeping planetary warming below 1.5°C
by the end of the century, the stretch goal
of the Paris pact, is now unlikely, analysts
say. Still, “We are in a different place now
compared to at the end of the Paris agree-
ment,” says Corinne Le Quéré, a climate
scientist at the University of East Anglia.
“No country is going fast enough, but many
countries are moving forward.” j
science.org SCIENCENEWS | IN DEPTH
ASTRONOMYInfluential U.S. wish list calls
for $11 billion space telescope
Decadal survey says NASA should be frugal and build
a series of optical, x-ray, and far-infrared observatories
By Daniel CleryA decadal survey found the 15-meter LUVOIR to be far too pricey; it called for a more modest 6-meter scope.