Without the hockey stick: Weather lessons from the Common

 

Without the hockey stick: Weather lessons from the Common Era

Significance

I am reviewing important developments, current challenges, and future indicators in the field of paleoclimatology of the Common Era since the publication of a unique curve "hockey stick" by the author and participants more than two decades ago, focusing on how paleoclimate data can inform our understanding of the impact of climate change man-made climate.

 

Summary

More than two decades ago, my coauthor, Raymond Bradley and Malcolm Hughes, and I were publishing a curve for the "hockey stake" now. It was a simple graph, available on large networks of various weather data ("multiproxy") data such as tree rings, ice cores, corals and lake carcasses, which captured the unprecedented environment of today's warmth. It became a place to focus on the debate on climate change created by humans and what they should do about it. However, the apparent simplicity of the hockey stick reflects the flexibility and complexity of climate history over the centuries and how it can enhance our understanding of human-induced climate change and its effects. In this article, I discuss the lessons we can learn from studying the paleoclimate records and the “Common Era” climate model, a period of two thousand years ago when the “sign” of human-induced warming increased dramatically after biodiversity.

 

Clearly, there is a cautionary tale identified by the hockey stick curve at unprecedented temperatures, but studies from the Common Era (CE) paleoclimate record go further. What can we do, for example, about the role of powerful mechanisms associated with the effects of climate change today from their previous response to natural drivers? Examples are the state of El Niño, the Asian summer rainfall, and the distribution of the North Atlantic conveyor belt. Are there any possible “tipping points” within these climate systems? How has sea level changed over the centuries, and what does it tell us about the future coastal danger? Is there a long-term environmental exposure, evident in the paleoclimate record, that could compete with man-made climate change today? Can we assess the "sensitivity" of the climate to sustainable human-induced growth in greenhouse gas emissions from assessing how the climate has responded to natural phenomena in the past? Also, can better estimates of past trends inform the test of how close we are to the critical “dangerous” temperature limits? In this article, I want to address such questions and provide ideas on how to convey confident answers.

 

Long stick, Sturdier Hockey

Twenty years since the beginning of Mann et al's "hockey stick" works. [1998 (1) and 1999 (2), commonly referred to as “MBH98” and “MBH99,” corresponding to the authors Mann, Bradley, and Hughes, respectively], dating back to 1000 CE, much of the details of paleoclimate is now available, sophisticated methods have been developed and applied to this data, and long-term reconstruction has been achieved using a low-resolution but high paleoclimate representative records. The result of the net is “the hockey wing” (3, 4) —a number of independent studies that come to the same conclusion as the long hockey stick (St. 1). Revised reconstruction shows that the recent warming has been unpopular in the long run, at least two thousand years ago and above, 20,000 y (5, 6) ago, rather than completed earlier than two decades ago by Mann et al. (2). Studies using climate models driven by a balanced environment (volcanic and solar) and anthropogenic forcing show that only the latter can explain this unprecedented warming trend (3).

 

Figure 1.

Comparison of the reconstruction of the temperatures including CE includes the original Mann et al. (2) reconstruction of the hockey stick (1, 2) and its 95% uncertainty list and various versions of the PAGES2k (Past Global Changes Last Two Millennium initiative) reconstruction (4) and the extent of uncertainty, and reconstruction of low decision Marcott et al. (5) and its uncertainty. Hadley Center and Climatic Research Unit Surface Temperature Product version 4 (HadCRUT4) of the global temperature series used is shown for comparison. RegEM refers to statistical reconstruction based on a standard expectation-enhancing process.

 

From the point of view of public discourse on climate change, these conclusions are important. They emphasize the enormous, unprecedented impact of human activity - especially on fuel - in our planet. From a scientific point of view, however, some of the most important details - details that really inspired the original work of MBH98 - include past variations and what they can tell us about climate change and responsiveness to foreign drivers or "forcibly." We examine this information in the next section.

 

Changing Methods and Responses

Many important impacts of climate change include climate change variables and their response to the imposition of anthropogenic climate. These include the El Niño / Southern Oscillation (ENSO), which influences global climate patterns, affecting the western US drought and the Atlantic hurricane among other things. This includes the closely related Arctic Oscillation (AO) or North Atlantic Oscillation (NAO), which affects the climatic conditions of North America and Eurasia. It includes the Asian summer rainfall where over one billion people depend on their access to clean water. Finally, there is the Atlantic Meridional Overturning Circulation (AMOC), often referred to as the “sea conveyor belt”. AMOC delivers warm water to the highlands of the North Atlantic, warming neighboring regions and circulating nutrients in the North Atlantic waters while pressing the seas off the US East C