Mhaze,

I’m aware of the myth that does the rounds among denialist circles about the “hockey stick” supposedly having been debunked, but it hasn’t. It did face scrutiny initially, but its main findings have since been vindicated by multiple studies employing different methods and data.

Multiple IPCC assessment reports that continue to use updated versions of the hockey stick graph to illustrate recent temperature trends. Additional studies also confirm the broad pattern observed by Mann et al. (which I’ve listed at the end of my reply).

Regarding Kaufman et al. (2009), this study focused on Arctic cooling and showed that the recent reversal of a long-term cooling trend is exceptional, aligning with broader evidence of unprecedented recent warming.

The PAGES 2k Consortium (2013) shows that the 20th-century warming is unprecedented over the past two millennia across multiple continents, supporting the idea that recent warming is not only regional but also global in nature.

Neukom et al. (2019) indicated that preindustrial warm and cold periods were not globally synchronised, unlike the current period where warming is observed globally, supporting the notion that current warming is unprecedented in its global coherence.

Abram et al. (2016) highlighted that industrial-era warming began in the mid-19th century and is unprecedented over the past 500 years, supporting the broader context of unusual recent warming.

The Schmidt et al. (2012): Here’s a working link http://gmd.copernicus.org/articles/5/185/2012.

Ljungqvist et al. (2012) reconstructed Northern Hemisphere temperatures and supported the finding that recent warming is unprecedented in the past 1,200 years, not 500. (Try this link: http://cp.copernicus.org/articles/8/227/2012)

The regional focus of some studies does not diminish the global implications of rapid recent warming, by the way.

Regarding Milankovitch cycles, these operate over millennia and indicate a long-term cooling trend. The rapid recent warming is inconsistent with these cycles, suggesting that another factor, namely anthropogenic greenhouse gas emissions, is driving current climate change. The mid-20th century cooling was influenced by increased aerosols from industrial activities, which temporarily masked the warming effect of CO2. Once air quality regulations reduced aerosol emissions, the underlying warming trend became more apparent.

(Cont'd)

As for the recent warming pause, short-term variability due to natural factors (like ocean heat uptake) can cause fluctuations in the warming rate. However, the long-term trend over the past century shows clear and significant warming, as confirmed by multiple datasets. Multiple studies indicate that the current rate and magnitude of warming are unprecedented not just in the past 500 years, but in the context of the past several thousand years.

Individual studies may have limitations or specific focuses, the cumulative evidence from a wide array of research supports the conclusion that recent global warming is unprecedented in its rate and magnitude. This conclusion is robustly supported by high-resolution modern data, multiple paleoclimate proxies, and advanced analytical techniques, highlighting the significant role of anthropogenic greenhouse gas emissions in driving recent climate changes. If you have evidence against this, then feel free to share it. I’m not aware of any.

Moberg et al. (2005) used a combination of low- and high-resolution proxies to reconstruct Northern Hemisphere temperatures over the past 2,000 years, supporting the unusual nature of recent warming (http://www.nature.com/articles/nature03265).

Mann et al. (2008) extended the original "hockey stick" reconstruction, incorporating a larger dataset and more advanced statistical methods, reinforcing the conclusion that recent warming is unprecedented over the past two millennia (http://www.pnas.org/content/105/36/13252).

Ljungqvist (2010) used a wide range of proxy data to show significant temperature variability over the past 2,000 years, highlighting the rapid warming of the 20th century as exceptional (http://onlinelibrary.wiley.com/doi/abs/10.1111/j.1468-0459.2010.00399.x).

The PAGES 2k Consortium (2013) compiled temperature reconstructions from seven continental regions, demonstrating that the recent warming is unprecedented over the past 2,000 years (http://www.nature.com/articles/ngeo1797).

Neukom et al. (2019) showed that previous warm and cold periods were not globally synchronous, contrasting with the coherent global warming observed in recent decades (http://www.nature.com/articles/s41586-019-1401-2).

"I’m aware of the myth that does the rounds among denialist circles about the “hockey stick” supposedly having been debunked,"

And there we go. It always reverts to name-calling when the data doesn't support the assertions. Oh, you don't buy the whole AGW theory so you must be a denialist.

You say the hockey stick wasn't debunked yet you yourself are acting like its debunked. The hockey stick's main purpose was to remove the Medieval Warm Period and the Little Ice Age from the record to try to then claim the uniqueness of the 20th century warming. Yet you've acknowledged the MWP and the LIA so you also don't accept the claims of MBH99. I won't bother assailing you with all the evidence advanced by the so many others (but most devastatingly McIntyre and McKitrick) but I'd remind you that after initially lauding MBH99 and using the graph in its reports, the IPCC couldn't drop it quickly enough when the facts came out.

Professor Jones of Oxford University:

"The Hockey Stick is obviously wrong. Everybody knows it is obviously wrong. Climategate 2011 shows that even many of its most outspoken public defenders know it is obviously wrong. And yet it goes on being published and defended year after year."

Again, you claimed it was unprecedented in human history but are unable to show that as a fact. Even if your claims about the last 2000 years were true, (and they're not) that's not human history. In the last 2000 years we've only had three periods of warming, and there's no evidence to show that the current one is any different to the other.

Just going back to something else in the paleo record you previously avoided. Marcott and many others have shown that the current temperatures have been exceeded 25% of the time in the past 12000 years. We continually get told of the dire results of these current high temperatures but somehow we survived the period with higher temperatures - indeed civilisation thrived.

But that gets swept under the carpet because it doesn't suit the narrative. Fear-mongering isn't science.

mhaze,

I didn’t call you any names, nor should I have felt any need to, given the overwhelming body of evidence in support of my claims (some of which I have linked you to). Speaking of which, though, the concept of denialism is legitimate and distinct from scepticism.

The "hockey stick" graph by Mann et al. (1999) did not aim to erase the MWP or the LIA. Its primary goal was to reconstruct past climate variability over the last millennium and to highlight how recent temperature increases compare to historical variations. The graph showed that while there were periods of regional warmth, such as the MWP, these were not as globally synchronised or as rapid as the recent warming observed in the 20th century.

This body of evidence (some of which I have linked to) supports the conclusion that the current warming is not only unprecedented in recent millennia but also poses significant risks due to its rapid rate and global extent, driven primarily by anthropogenic greenhouse gas emissions. Simply, denying that I have provided evidence and repeating unfounded myths about the “hockey stick” is not a rebuttal. You need to explain why the evidence doesn’t support the conclusion.

Once again, numerous studies indicate that the current rate and magnitude of warming are exceptional in the context of the past several thousand years. As just one example, Ljungqvist et al. (2010) reconstructed temperatures for the Northern Hemisphere over the past 2,000 years, highlighting the exceptional nature of recent warming. While the last 2,000 years may not cover the entirety of human history, it includes significant periods of human civilization, providing a relevant context for understanding the impact of recent climate changes (which is what I meant previously by, “in the context of human history”).

Your claim that Marcott et al. (2013) and others have shown that current temperatures have been exceeded 25% of the time in the past 12,000 years and that civilizations thrived during those periods lacks nuance. Marcott et al. (2013) reconstructed global temperatures over the Holocene using a variety of paleoclimate proxies.

(Cont’d)

(Cont’d)

The study found that recent temperatures are indeed comparable to, or slightly higher than, the warmest periods of the Holocene. However, the key difference lies in the rate of change. The current rate of warming is unprecedented within the context of the Holocene epoch.

Warm periods in the Holocene were often driven by gradual changes in Earth's orbit (Milankovitch cycles), solar radiation, and natural CO2 fluctuations. These changes occurred over thousands of years, allowing ecosystems and human societies to adapt gradually. The rapid warming observed in recent decades, driven by anthropogenic greenhouse gas emissions, is occurring at a much faster rate than any natural warming observed in the past 12,000 years.

The claim that temperatures have been exceeded 25% of the time in the past 12,000 years may refer to regional temperature peaks rather than a globally averaged context. Marcott et al. (2013) indicated that while there were warmer periods in specific regions, the global average temperatures and the rate of current warming are unprecedented. One of the crucial aspects highlighted by Marcott et al. is the unprecedented rate of current warming. Even if certain periods had similar peak temperatures, the current rate of temperature increase is much faster, which has significant implications for both natural and human systems.

Human civilizations have thrived during warmer periods in history, but these changes were gradual, allowing societies to adapt over centuries or millennia. The rapid pace of current warming poses a unique challenge. Infrastructure, agriculture, water resources, and ecosystems are being forced to adapt to changes that are happening over decades rather than centuries. The current rapid warming has already led to more frequent and severe weather events, rising sea levels, and shifts in climate zones, which were not experienced during past warm periods. Modern civilization is highly interconnected and dependent on stable climate conditions for food production, water supply, and infrastructure stability. Rapid climate changes threaten these systems in ways that were not a concern for ancient civilizations.

Nothing is being swept under the carpet. Please let me know if there is anything else I have “avoided”.

"The "hockey stick" graph by Mann et al. (1999) did not aim to erase the MWP or the LIA.

Well that's not what was said at the time. Leading up to the MBH99 the climate community had been upset at the way the people they called deniers were using the MWP/LIA to show natural fluctuations in temperatures. Climategate emails show them saying ... “We have to get rid of the Medieval Warm Period.” MBH99 was embraced because it did that.

Mann claims more recent research supports his claims about these periods, but most recent reconstructions reinstate the MWP/LIA.

" As just one example, Ljungqvist et al. (2010) reconstructed temperatures for the Northern Hemisphere over the past 2,000 years, highlighting the exceptional nature of recent warming. "

Well that's not true. First they only looked at extra-tropical NH. They found a Roman Warm Period (RWP), a Dark Ages cool period, a Medieval Warm Period and the LIA. They specifically say the RWP was similar to the most recent temperatures. They specifically say that temperatures in the MWP exceed those currently occurring. They specifically say the temperatures of the MWP were likely higher than any other time in the last 2000 years. They specifically say that the data remains too fragmentary to make claims on decadal levels which was my point all along.

"The study [Marcott13] found that recent temperatures are indeed comparable to, or slightly higher than, the warmest periods of the Holocene. However, the key difference lies in the rate of change. The current rate of warming is unprecedented within the context of the Holocene epoch."

Well that's just wrong. Marcott specifically said that they are higher than 75% of the Holocene ie lower than 25% of the Holocene. (" Current global temperatures of the past decade have not yet exceeded peak interglacial values but are warmer than during ~75% of the Holocene temperature history.")

Whatismore, Marcott specifically said in supplements to the study that the data wasn't good enough to show if the current warming is unprecedented.

/cont