(04-05-2024, 09:27 PM)pianopraze Wrote: I’m much more worried about the coming ice age.

Nimoy said it so I believe it!

(03-31-2024, 08:02 PM)argentus Wrote: Instead of mandating "no single-use plastics", we should be working on reusing and repurposing those plastics.

(05-01-2024, 04:39 PM)Maxmars Wrote: I only wish that the business paradigm in our country wasn't solely centered on profit growth.  You see, like many other great ideas, if it won't make the rich richer, it's not considered "viable business" and must be marginalized if not utterly destroyed - as a waste of 'resources.'

Quote:AbstractThe North Atlantic was a key locus for circulation-driven abrupt climate change in the past and could play a similar role in the future.

Quote: The climate system is capable of abrupt changes when a threshold is crossed that shifts the climate system into a different state (National Research Council, 2002). Because of the potential for abrupt change in the near future (e.g., Lenton, 2011)—and the heightened societal vulnerability to rapid rates of climate change—examples of abrupt climate change in the paleorecord are particularly important to understand (Alley et al., 2003; Broecker, 2000). The sudden reduction or shutdown of Atlantic Meridional Overturning Circulation (AMOC), which is responsible for the transport of low-latitude heat to the Arctic, is a known mechanism for abrupt climate change (Broecker, 1991; Clark et al., 2002; Sgubin et al., 2017). A sudden influx of freshwater in key downwelling sites (e.g., the Labrador Sea) can effectively slow or shut down AMOC, reducing latitudinal heat transport and thus promoting high-latitude cooling.

Quote: A forthcoming collapse of the Atlantic meridional overturning circulation (AMOC) is a major concern as it is one of the most important tipping elements in Earth’s climate system[sup]1,2,3[/sup]. In recent years, model studies and paleoclimatic reconstructions indicate that the strongest abrupt climate fluctuations, the Dansgaard-Oeschger events[sup]4[/sup], are connected to the bimodal nature of the AMOC[sup]5,6[/sup]. Numerous climate model studies show a hysteresis behavior, where changing a control parameter, typically the freshwater input into the Northern Atlantic, makes the AMOC bifurcate through a set of co-dimension one saddle-node bifurcations[sup]7,8,9[/sup]. State-of-the-art Earth-system models can reproduce such a scenario, but the inter-model spread is large and the critical threshold is poorly constrained[sup]10,11[/sup]. Based on the CMIP5 generation of models, the AR6 IPCC report quotes a collapse in the 21st century to be very unlikely (medium confidence)[sup]12[/sup]. Among CMIP6 models, there is a larger spread in the AMOC response to warming scenarios, thus an increased uncertainty in the assessment of a future collapse[sup]13[/sup]. There are, however, model biases toward overestimated stability of the AMOC, both from tuning to the historic climate record[sup]14[/sup], poor representation of the deep water formation[sup]15[/sup], salinity and glacial runoff[sup]16[/sup].

Quote: The AMOC has only been monitored continuously since 2004 through combined measurements from moored instruments, induced electrical currents in submarine cables and satellite surface measurements. Over the period 2004–2012, a decline in the AMOC has been observed, but longer records are necessary to assess the significance. For that, careful fingerprinting techniques have been applied to longer records of sea surface temperature (SST), which, backed by a survey of a large ensemble of climate model simulations, have found the SST in the Subpolar gyre (SG) region of the North Atlantic (area marked with a black contour in Fig. 1a) to contain an optimal fingerprint of the strength of the AMOC.

Quote: Anomalously high summer temperatures over the last few decades have resulted in sharply increased mass losses of glaciers and ice caps in the Canadian Arctic Archipelago (CAA), particularly since 2005 (Gardner and others, Reference Gardner2011; Harig and Simons, Reference Harig and Simons2016). Between 2003 and 2009, glaciers and ice caps of Baffin and Bylot Islands in the southern CAA lost mass at an area-averaged rate 1.6 times greater than glaciers in the northern CAA (Gardner and others, Reference Gardner, Moholdt, Arendt and Wouters2012). Projections by a coupled atmosphere/snow model forced with the IPCC's moderate RCP4.5 greenhouse gas emission scenario forecast sustained and irreversible glacier mass losses in the CAA, increasing from −51 ± 26 Gt a[sup]−1[/sup] over the period 2000–11 to −144 ± 33 Gt a[sup]−1[/sup] by the end of the 21st century, resulting in a projected 18% loss of the current ice volume (Lenaerts and others, Reference Lenaerts2013).
A major unresolved question in assessing the response of Arctic glaciers to climate change is whether they will speed up or slow down as surface melt rates increase. Observations of short-term, high velocity events on some parts of the Greenland ice sheet (GIS) in summer (Zwally and others, Reference Zwally2002) have led to concerns that accelerated ice motion may occur as the climate warms and surface melt rates increase. In turn, this could produce dynamic thinning (Alley and others, Reference Alley, Clark, Huybrechts and Joughin2005) and greater drawdown of ice from the interior, resulting in increasing mass wasting rates in response to future warming (Parizek and Alley, Reference Parizek and Alley2004). Several studies support the short-term speedup mechanism initially proposed by Zwally and others (Reference Zwally2002), in that delivery of surface meltwater to the ice-sheet bed results in an over-pressurized basal drainage network, reduced basal friction and a short-term increase in ice motion. For example, Bartholomew and others (Reference Bartholomew2012) measured pronounced multiday speedup events inferred to be forced by rapid variations in meltwater input to the subglacial system from diurnal and weather-related fluctuations. Similarly, Fitzpatrick and others (Reference Fitzpatrick2013) measured a dramatic acceleration (100% over 11 days) on the lower portion of an outlet glacier, located on the western sector of the GIS, 4 days after the onset of melt. Similar positive relationships between melt and short-term velocity variations have been observed on temperate and polythermal valley glaciers (Iken, Reference Iken1981; Mair and others, Reference Mair2003; Copland and others, Reference Copland, Sharp, Nienow and Bingham2003b) .
However, other recent studies indicate that the relationship between increased surface melt rates and glacier velocities is not straightforward. For example, Sundal and others (Reference Sundal2011) found a positive correlation between surface melt rates and peak velocities during early summer (~May to mid-July) for land-terminating glaciers in southwestern Greenland over a 5 year period, but found that mean summer velocity was lower during high melt years. A slow-down occurred when a critical amount of meltwater entered the ice sheet, causing a switch to a channelized subglacial drainage network. In years with high surface melting this switch occurred earlier in the summer, resulting in lower mean summer ice velocities compared with years with less melt. Simulations using subglacial hydrology models support this pattern as they show that when the subglacial water inputs exceed a critical rate, subglacial channelization occurs rapidly (Schoof, Reference Schoof2010; Banwell and others, Reference Banwell, Hewitt, Willis and Arnold2016). Other studies have identified a relationship between high summer melt rates and the evolution of a more efficient subglacial drainage system, which results in lower velocities the following winter (Burgess and others, Reference Burgess, Larsen and Forster2013; Sole and others, Reference Sole2013; Tedstone and others, Reference Tedstone2013). Long-term (≥8 years) ice motion measurements from a land-terminating region of the western GIS (Tedstone and others, Reference Tedstone2015) and many other non-surging glaciers elsewhere (van de Wal and others, Reference van de Wal2008; Heid and Kääb, Reference Heid and Kääb2012b; Waechter and others, Reference Waechter, Copland and Herdes2015; Thomson and Copland, Reference Thomson and Copland2017) also reveal decreasing ice velocities despite an overall increase in temperature and surface melt rates.

Quote: The Gulf Stream is a surface current that flows up the east coast of the US then crosses the Atlantic to Europe, carrying warm tropical water with it. This warm water releases heat into the atmosphere, warming Europe.
 
The researchers found that during the last ice age, when ice sheets covered much of the northern hemisphere, stronger winds in the region resulted in a stronger and deeper Gulf Stream. However, despite the stronger Gulf Stream, overall, the planet was still much colder than today.
 
Lead author Dr Jack Wharton (UCL Geography) said: “We found that during the last ice age, the Gulf Stream was much stronger because of stronger winds across the subtropical North Atlantic. As a result, the Gulf Stream was still moving lots of heat northwards, despite the rest of the planet being far colder. Our work also highlights the Gulf Stream’s potential sensitivity to future changes in wind patterns. For example, if in the future winds are weaker, as shown in a recent study using climate models, it could mean a weaker Gulf Stream and a cooler Europe.”
 
The Gulf Stream is also part of the vast Atlantic Meridional Overturning Circulation (AMOC), which is driven by both deep water formation in the subpolar North Atlantic, where cooling causes surface waters to become dense and sink, as well as winds. Scientists have previously raised concerns about how climate change could weaken the AMOC as melting glacial water pouring off Greenland could disrupt deepwater formation, preventing warm tropical water from reaching Europe and thus cooling the continent.
 
Together, the combined effect of weakening winds and reduced deep water formation could significantly weaken the Gulf Stream. If the AMOC were to collapse – considered an unlikely but possible future scenario - European temperatures would cool by 10 to 15 degrees Celsius, wreaking havoc on continental agriculture and weather patterns, and the decrease in the wind-driven part of the Gulf Stream would further exacerbate this.

Quote: An ambitious effort to understand the Earth’s climate over the past 485 million years has revealed a history of wild shifts and far hotter temperatures than scientists previously realized — offering a reminder of how much change the planet has already endured and a warning about the unprecedented rate of warming caused by humans.
 The timeline, published Thursday in the journal Science, is the most rigorous reconstruction of Earth’s past temperatures ever produced, the authors say. Created by combining more than 150,000 pieces of fossil evidence with state-of-the-art climate models, it shows the intimate link between carbon dioxide and global temperatures and reveals that the world was in a much warmer state for most of the history of complex animal life.
 
At its hottest, the study suggests, the Earth’s average temperature reached 96.8 degrees Fahrenheit (36 degrees Celsius) — far higher than the historic 58.96 F (14.98 C) the planet hit last year.
 
The revelations about Earth’s scorching past are further reason for concern about modern climate change, said Emily Judd, a researcher at University of Arizona and the Smithsonian specializing in ancient climates and the lead author of the study. The timeline illustrates how swift and dramatic temperature shifts were associated with many of the world’s worst moments — including a mass extinction that wiped out roughly 90 percent of all species and the asteroid strike that killed the dinosaurs.

Quote:At the timeline’s start, some 485 million years ago, Earth was in what is known as a hothouse climate, with no polar ice caps and average temperatures above 86 F (30 C). The oceans teemed with mollusks and arthropods, and the very first plants were just beginning to get a toehold on the land.
 
Temperatures began to slowly decline over the next 30 million years, as atmospheric carbon dioxide was pulled from the air, before plummeting into what scientists call a coldhouse state around 444 million years ago. Ice sheets spread across the poles and global temperatures dropped more than 18 degrees Fahrenheit (10 degrees Celsius). This rapid cooling is thought to have triggered the first of Earth’s “big five” mass extinctions — some 85 percent of marine species disappeared as sea levels fell and the chemistry of the oceans changed.

Quote:An even more dramatic shift occurred at the end of the Permian period, about 251 million years ago. Massive volcanic eruptions unleashed billions of tons of carbon dioxide into the atmosphere, causing the planet’s temperature to shoot up by about 18 F (10 C) in roughly 50,000 years. Acid rain fell across the continents; marine ecosystems collapsed as the oceans became boiling hot and depleted of oxygen.
 
“We know it to be the worst extinction in the Phanerozoic,” Tierney said. “By analogy, we should be worried about human warming because it’s so fast. We’re changing Earth’s temperature at a rate that exceeds anything we know about.”
 
The study also makes clear that the conditions humans are accustomed to are quite different from those that have dominated our planet’s history. For most of the Phanerozoic, the research suggests, average temperatures have exceeded 71.6 F (22 C), with little or no ice at the poles. Coldhouse climates — including our current one — prevailed just 13 percent of the time.