Reefer Panic

Oh, this again.

Hudema is somewhat right, this statement, and somewhat the graphic, does come directly from the UN IPCC. It’s right here in the Summary for Policymakers of IPCC Special Report on Global Warming of 1.5°C approved by governments published in 2018.

Coral reefs would decline by 70-90 percent with global warming of 1.5°C, whereas virtually all (> 99 percent) would be lost with 2°C.

The graphic is actually a combination of two separate graphics, cropped to remove the citation from an October 2020 UN IPCC press/puff release, Why Actor Edward Norton Champions Biodiversity (special episode).

It’s too bad Hudema either didn’t have the original graphics, or cropped out the first image in the panel itself as it would further “support” his latest panic with the “every fraction of a degree matters” quote.

That link above, confusingly, isn’t even the full Summary for Policymakers from the 2018 Special Report on 1.5c.

That’s here and the full Chapter 3 where the reefs are discussed in extreme detail is here in the Impacts of 1.5°C of Global Warming on Natural and Human Systems chapter.

Confusion around the various IPCC reports isn’t nothing new and it’s something I tried to address years ago.

But there’s also confusion about these two temperature “targets.” The IPCC, and parroters such as Hudema imply a global temperature shift due to climate change will increase from 1.5°C to 2.0°C and with each increase [insert catastrophe] here will happen.

The 2°C target has its roots in a quasi-scientific exercise by the German Advisory Council on Global Change (WBGU) in 1995, tied to a "tolerable temperature window" derived from historical climate data (the last ice age and interglacial periods). It was a heuristic attempt to set an upper limit, pegged at roughly 2°C above pre-industrial levels, and became entrenched as a policy anchor over time.

The 1.5°C target, on the other hand, emerged later and driven by political advocacy rather than a scientific reassessment. By the time of the 2015 Paris Climate Agreement negotiations, small island states and vulnerable nations argued that 2°C wasn’t safe enough, pushing for a stricter goal. In other words, this wasn’t born from new climate data or a refined understanding of scientific evidence—it was a diplomatic response to equity concerns, later backfilled with modeling efforts that leaned on speculative assumptions (e.g., negative emissions technologies).

The 1.5 Degree Temperature Target is a Dead Man Walking

The Two Degree Temperature Target is Arbitrary and Untethered

Using them together, as the climate hysterics do with its phrasing of "well below 2°C" while "pursuing efforts" toward 1.5°C, is problematic for a few reasons:

First, the two benchmarks emerge from different foundations. The 2°C target at least started with a (now outdated) scientific rationale, however loose, while 1.5°C was a essentially a political add-on. Pairing them together is muddy —neither is a clear, evidence-based line in the sand, but they’re treated as if they’re equally grounded.

Second is inconsistent feasibility. Pielke notes that 1.5°C pathways require extreme, often unrealistic mitigation measures, while 2°C was historically seen as more achievable. Pursuing both simultaneously creates a split focus—policy shifts between an aspirational ideal and a slightly less impractical ceiling, diluting clarity on what’s actually possible.

Third, is shifting of goalposts: If the WBGU’s original logic were updated with modern IPCC data, the "tolerable" limit might drop to 1°C, not 2°C as Pielke also noted. Meanwhile, 1.5°C was grafted on without revisiting that original framework. This mismatch shows how the targets don’t cohere as a unified scientific story—they’re patched together from different eras and motivations.

In other words, their dual use is awkward. They’re not complementary scientific benchmarks but rather separate processes—one an aging analytical guess, the other a negotiated compromise. Treating them as a cohesive pair papers over these cracks and both make a mockery of the scientific method.

This doesn’t necessarily refute the scientific evidence suggesting that reefs may be indeed in danger but it complicates the story because they’re linked to numbers selected for political impact rather than ecological accuracy.

This combination of science and politics means we should critically evaluate such claims: the situation for reefs is likely indeed dire and worsening, but the precise temperature at which they reach a tipping point of irreversible decline isn’t as precisely tied to 1.5°C or 2°C as the UN’s fear pieces or Hudema suggests.