About once a day, someone tells me that human caused climate change is not real because this or that thing in the latest report by the Intergovernmental Panel on Climate Change (IPCC) contradicts something I, or some other scientists or science writer, has said.

I’ve noticed an uptick in references to the IPCC report by those intent on denying the reality of climate change. This even happened at recent congressional hearings, where “expert witnesses” made similar claims.

How can that be? How can the flagship scientific report on climate change, the objective source of information about the science of climate change, be used so frequently to argue that scientists have climate change all wrong?

Obviously, one way this can happen is if the information is cherry picked or misrepresented. That, certainly, happens and is almost always part of the recipe. But there is another only barely less obvious reason, and this is a reason that becomes more and more relevant every passing year. What is it? Hold on a sec, first a bit of context.

As a scientists and writer-about-science I often have access to temporarily secret information. Also, I make it a point to keep track of opinions held by trusted experts in the field, as they change and adapt to new findings. This secret information is, of course, peer reviewed research that isn’t published yet, and is under embargo.

To be embargoed means to be held in secret, but distributed to a small number of trusted individuals or agencies (often news outlets and science writers), with an “embargo date and time” after which the information is no longer secret. There are a few reasons this is done. One is that many scientific outlets rely on the splash factor to get readership, and having a paper that changes how we think about the world be released at a particular planned moment helps with that. Related is the idea that publishers, research institutions, and the scientists themselves want the paper published alongside other products to help the press and the public understand the material better, such as a press release, selected graphics, maybe a nice video. This all requires production time and effort, and it is pretty much wasted effort if it does not become publicly available at the same exact moment the paper becomes available.

A few papers exist as early drafts long before publication, and those are passed around for the purpose of getting some preliminary feedback, and to get the conversation about the topic going among experts. That is less common because many journals don’t like it, and how often this happens depends on the field of study. Indeed, there are entire “journals” that started as and still serve as semi-formalized outlets for early drafts of appers, academic theses, or reports are routinely published, sometimes years before a final peer reviewed product comes out, representing for example that year’s output from a long term grant. (NBER and BAR come to mind as examples of this.)

Authors and publishers send me embargoed papers they think I might want, or more commonly, ask me if I’d like to have a copy of an embargoed paper, giving me a chance to say yes. Often, I know of a subset of scientists who also have the paper (typically, the co-authors) and I can ask them questions about the paper before hand. Most outlets will provide a science writer with this sort of contact information. This is how all those fully formed news reports come out in the media the moment a paper is released. Days or even weeks of work has already happened, quietly and in secret, before the paper’s release.

Other research is available in other ways. I have colleagues who are always working on certain things, and they’ll say things like, “well, we don’t have it finalized yet, but this thing you said is probably wrong because X turns out to be larger than Y, even though we previously thought the opposite … we’ve got a paper coming out probably next summer on this…” or words to that effect.

All this is, of course, why I write the blog posts and you read them. You could do this too; You could have foreknowledge of the developments on the leading edge of a particular scientific field as well. You just have to become a credible quasi-journalistic outlet (I am not now nor have I ever been a journalist) and develop a pertinent Rolodex, and gain the trust of everybody. Takes a few years.

I mention all this because it makes this happen now and then: I have a concept of some aspect of climate change research that is not yet generally understood outside a limited range of experts. Then, of course, the dissemination of information catches up and everybody knows the same thing, and the revised, updated view of that bit of science is now added to general knowledge. Close behind, perhaps, follows a shift in, or refinement of, consensus. This is how science works large scale.

The scientific understanding of an active area of research is dynamic and requires currency. Six months old is old. A year or two old is ancient.

I’ll give you three examples.

A while back the generally understood consensus of sea level rise was that sea levels were going up at a certain relatively low rate, on average. However, that estimate was faulty because of a lack of integration of a full understanding of how water moves between fresh water reservoirs and the sea, and certain really cool research on ocean warming, gravitational effects, etc. had not yet been published. Also, some time was missing; there had been a couple of strange quirky sea level related events that turned out to be outliers, so data sets needed to be full updated, and a couple of years added over the passage of time. For this reason, what was generally known at one point in time was different from what came to be understood a few years later. People in my position saw it coming, people who were not tracking the literature held the old and incorrect view.

Second and related example: There was a set of estimates for how fast glaciers in polar regions (Greenland and Antarctica) would melt with global warming, and how much this process would contribute to sea level rise. However, there was some new research coming to bear on the issue that was starting to change that. Glaciers don’t just melt, but they also structurally fall apart, big chunks ending up in the sea and melting there. Some increase in understanding how that happens emerged. The upper limit of how fast that could probably happen, in the general publicly available knowledge base, was modest. But over a fairly short period of time, a previously highly speculative and closely held thought that the upper limit on how much ice could deteriorate was higher, and a similarly unexpressed thought that the lower limit on how soon that might start to happen, began to make its way into the more public discussion. This is still very much an area of uncertainty and very active research. Look for big changes and many surprises over the next 24 months. But today, the best informed experts have a very different view of what might happen, and what is likely to happen, than widely held a few years ago, because of this shift. Polar glaciers will likely fall apart and contribute to sea level rise more and sooner than the best guesses would have suggested five years ago.

A third example just went through a major change. A few years ago it was generally thought, and often repeated, that it was difficult to attribute human caused climate change as a reason behind any particular bad weather event. That has shifted dramatically over time. A set of studies a few years back failed to find any clear association in a majority of weather events. A year later, a similar number of studies, of new weather events, either attributed the events to climate change or resulted in “we can’t say one way or another.” The most recent papers are generally showing a likely connection. Meanwhile, certain research linking certain climate phenomena to a large set of bad weather events was developing. Note that the previous studies were conducted mainly ignoring this new and emerging research. I was a little like saying “We don’t know why so many more people are falling on the subway tracks these days” while ignoring a growing set of observations of bad people showing up at the subway stations and pushing people off the tracks on purpose. In the absence of consideration of this nefarious and willful behavior, one could not say that the increase in untoward events was anything other than a random uptick in numbers. Seeing and acknowledging an actual cause makes it impossible to not link the cause and effect.

This happened, as noted, slowly and in the background in the literature, and suddenly, just a few days ago, a crowing paper took that likely cause of severe weather, ran it in highly sophisticated and reliable models, and demonstrated that this is a thing. Humans release fossil carbon in greenhouse gasses (and do some other bad things), certain things about our climate system change unambiguously because of this, this causes an important but heretofore not fully understand change, which then causes additional droughts and floods across the globe.

Five years ago, that would have been regarded as speculation, worthy of consideration but nothing that could nail down our understanding of the greenhouse gas – severe weather link. Today, the link is sufficiently established to regard it as scientific fact rapidly becoming consensus, though there will certainly be a bit more fighting about it, and much refinement of the theory and data.

All of these examples can be rephrased in relation to the last IPCC report.

The most recent IPCC report was published nominally in 2014. It was restricted to existing peer reviewed literature, thus not including the pre-embargoed material (though there was an effort by many scientists to get stuff out in time to be employed in that process). The report took time to produce. The physical science basis part of the report, on which the rest is based, actually dates to 2013 nominally, though it includes some 2014 material.

It is now April 2017. A claim that “The IPCC Report said bla bla bla therefore you are wrong” is the same as “in or before 2013, at least 4 years ago, the best we knew was bla bla bla therefore your are wrong.

Let’s return to the sea level rise example and consider the thinking of how fast and how much glacial melting, and other factors, would cause sea levels to rise in the future.

There were several studies used in the IPCC report, mostly dating to or before 2011. I would regard the science in the IPCC report to reflect the thinking primarily of the first decade of the 21st century on this subject. The last 2 years, or even one year, of research on sea level rise contrasts remarkably with that early work, suggesting a faster rise and more of it. That is just what is published. I don’t happen to know of any new work coming out shortly, but I can promise you that the summaries, the estimates, and the graphics that would be produced by an IPCC-like agency working on a summary of the physical science of sea level rise as it stands right now would be significantly different than what the last such report by the actual IPCC provided in 2014.

Two IPCC reports back, it was estimated that global sea level could rise between 18 and 59 cm by 2100. The subsequent report, the most current one, estimated that sea levels can rise between 29 and 82 cm by 2100. A recent and well regarded paper, dating to early in 2016, and using the best available information and methodology, estimates that the global sea level could rise by more than a meter by 2100 from just the melting of Antarctic, not counting Greenland.

Longer term sea level rise estimates have also risen, with a key paper published in 2013 suggesting that we may be in for as much as two meters over the next few centuries, and the aforementioned most recent report suggesting “more than 15 metres by 2500.”

(I hasten to add that an estimate of between 8 and 15 meters has been on the table for a long time, coming from palaeoclimatologists, who have always seen higher levels because in the past, similar conditions today produced such high levels, indicating that current levels are actually unusually low.)

Climate science is progressing very rapidly, especially in some areas. There are things we know now, or that we feel fairly comfortable asserting as pretty likely, that one year ago, and certainly four years ago, were fairly uncertain or in some cases inconceivable.

Citing the most recent IPCC report about a climate change relate issues tells me two things:

1) You don’t read the literature or talk to climate scientists; and

2) You are not especially interested in an honest conversation about this important scientific and policy issue.

The recent work on sea level mentioned above is here, the IPCC report is here, and a summary of the IPCC and other sources is here.