I've got to say that I'm really disappointed in the recent discourse surrounding the RCP8.5 scenario. The lack of context and understanding is something I expected from the usual suspects, but it's frustrating to see such bad takes from people and outlets who should know better.

Today, it's clear that specific *socioeconomic* storyline embedded in RCP8.5--essentially, a "burn all the coal" scenario--was unlikely even at inception & later became even less so. I do agree that this context could have been communicated better. But therein lies the rub.

Many folks are forgetting what the "8.5" stands for in "RCP8.5." It refers to a top-of-the-atmosphere radiative forcing of 8.5W/m2--essentially a very strong human-caused global warming influence that would cause extreme planetary warming.

There is, in real world climate system, more than one path to get to a "high warming scenario." Thankfully, it doesn't look like we're going to take anything close to an RCP8.5 *emissions* trajectory. But that does not mean we're safe from an RCP8.5-like level of warming. Why?

The main reason: It's still possible that the Earth system is more sensitive to a given level of greenhouse gas increase/aerosol decrease than previously was assumed and, thus, could warm more than indicated in historical IPCC scenarios even with a lesser degree of GHG increase.

In fact, there is recent evidence this may be the case! Some combination of changes to cloud patterns, aerosol effects, & biosphere carbon cycle feedbacks does appear to be putting us in the upper half of predicted range of Earth system sensitivity (exactly how high remains TBD).

This, ultimately, is the key to understanding why RCP8.5, and other past/present "high warming" scenarios, were and remain scientifically useful and have not been "overturned" in any meaningful sense.

High warming scenarios, whether RCP8.5 or otherwise, have mainly been used in "sensitivity experiments," asking questions about what the global climate system would look like a very high warming levels and what the impacts of that very high level of warming might be.

High warming scenarios have also been used to examine changes & impacts *along a wide spectrum of warming.* If only using a low warming scenario in an experiment, one can only assess low warming outcomes. High warming scenarios allow for consideration of full range of impacts.

I will once again reiterate that this usage could have been communicated better! There were certainly studies, and headlines, that did not adequately characterize use of RCP8.5 in this manner. That is a valid *science communication* criticism. But it misses the bigger picture...

There's absolutely nothing scientifically wrong with conducting "large signal" sensitivity experiments. In fact, it's a fundamental approach used across disciplines to distinguish signal from noise! And it's disappointing to see pundits who should understand this claim otherwise.

So, setting aside the frustrating RCP8.5 discourse for a moment, where do we actually stand in terms of our global warming trajectory as it's currently best understood by science and scientists?

We currently appear to be taking an upper mid-range greenhouse gas emission trajectory through the late 2020s relative to IPCC scenarios from 10-20 years ago (i.e., not an extremely high RCP8.5-like one, certainly, but also not an especially low one--closer to RCP4.5 or RCP6).

That could, and hopefully will, change moving forward as we accelerate bending the carbon curve toward lower carbon emissions in the coming decades. But it has not happened as quickly as many have hoped and some have assumed. Predicting human behavior, and geopolitics, is hard!

Ultimately, the Earth could still experience RCP8.5-like warming this century even though RCP8.5-like emissions are virtually impossible. It's not likely, but it's within realm of possibility. That's alarming, and it means we absolutely need to understand potential consequences.

Today, there are newer "high warming" scenarios that do not involve such implausible socioeconomic/emissions storylines as did RCP8.5. That's good! But it's also pretty irrelevant for climate science studies focused on investigating still-possible high-warming outcomes.

A lot of people who should know better are treating the demise of RCP8.5 as some kind of "gotcha!" moment that somehow overturns the rather dire climate predictions of the past decade. In reality, nothing could be further from the truth!

There are currently serious scientific debates unfolding regarding whether the Earth could ultimately warm *more* than previously expected, and/or whether certain key climate change impacts could unfold earlier than expected, even as our estimates of future emissions decline.

The basic science behind global warming remains, as has been said, "settled." But there are legitimately many questions still to answer, and some of them are potentially consequential. Uncertainty in this space is decidedly not our friend, and we should not presume it as such.