This is true and contradicts the article title and focus on a the past decade (really since 2013) of slower rates of ice mass loss.

But still extremely negative ice mass balance.

This is a really simplistic interpretation that negates physics of glacial ice and its response to annual ocean and atmospheric temperatures. The non-linear response of the Greenland Ice Sheet to warming and the lag time between, for example, a warm month or couple of months and ice mass loss means that there are asynchronous changes in climate and ice mass balance.

Rather than extrapolating cumulative ice loss, a peer-reviewed study that uses fine-scale ice sheet model with uncertainty quantification indicates the Greenland Ice Sheet could disappear entirely in 1,000 years.

Aschwanden, A., Fahnestock, M. A., Truffer, M., Brinkerhoff, D. J., Hock, R., Khroulev, C., ... & Khan, S. A. (2019). Contribution of the Greenland Ice Sheet to sea level over the next millennium. Science advances, 5(6), eaav9396.

The data reflect major losses of ice, via ice thinning, ice mass loss, and accelerated ice discharge, despite a lower magnitude of overall ice mass loss since 2013; but the mass balance is still negative and on track (based on the multi-decadal trend) to continue to loss mass.

This headline reflects a major finding of a peer-reviewed study.

Briner, J. P., Cuzzone, J. K., Badgeley, J. A., Young, N. E., Steig, E. J., Morlighem, M., ... & Nowicki, S. (2020). Rate of mass loss from the Greenland Ice Sheet will exceed Holocene values this century. Nature, 586(7827), 70-74.

The rate of ice mass loss has decreased since 2013, yet the annual loss of ice is still considerable and reflects the long-term impact of atmospheric warming and ice dynamic response to such.

Shepherd, A., Ivins, E., Rignot, E., Smith, B., Van Den Broeke, M., Velicogna, I., ... & Wuite, J. (2020). Mass balance of the Greenland Ice Sheet from 1992 to 2018. Nature, 579(7798), 233-239.

I am not aware of previously unidentified islands revealed by melting events in Antarctica.

It is important to note for all media outlets that contacting scientists regarding discoveries made in the field or on the ship while in Antarctica is extremely difficult due to limited to no internet access. While on the ship, scientists do not have access to their institutional email accounts.

This is not true, and was not stated by Dr. J.S. Wellner.

This is true based on preliminary visual identification of rocks sampled on the island.

False.

It is true that reduced ice load on the solid Earth leads to land rebound; however, it is not true or even plausible that a single record warm day is responsible for island discovery (possibly due to emergence or simply ice shelf retreat) 2,000 kilometers away.

To my knowledge, the record daily temperature is not responsible for widespread melt of glacial ice in the northern Antarctic Peninsula and certainly not an immediate retreat response in the local glacial systems.

The record temperature was recorded as one measurement and not a part of a long-term measurement dataset.

The island reference here is near Pine Island Bay in the Amundsen Sea, over 2,000 kilometers away from Seymour Island where the record air temperature was recorded. For reference, attributing the new-found island in Pine Island Bay to air temperature at Seymour Island would be like blaming heavy rainfall in Austin, Texas to air temperature in Los Angeles, California.

Because this island has just been identified and its history is completely unknown, we don't know if it emerged from below sea level to above sea level by a process called glacial isostatic adjustment, or the floating ice shelf has simply retreat from the island. Regardless, based on historical satellite imagery, the island seems to have been uncovered in the early 2010s. Much work is needed to confirm whether the island emerged from beneath sea level or was deglaciated by the ice shelf retreating landward off the island.

The record air temperature occurred on Seymour Island in the Antarctic Peninsula, over 2,000 kilometers from the uncharted island.

More accurate to say 'it could get worse'

It is generally true that conditions are suitable for irreversible collapse of the West Antarctic ice sheet via the process called 'Marine Ice Sheet Instability' where an initial forcing of ice sheet retreat progresses inland due to a landward-sloping bed that forces marine-based ice sheets to retreat into yet deeper and deeper water. However, there are potential brakes that could halt this 'irreversible' retreat including bumps in the bed topography that the ice is sitting on top of that can act as pinning points as well as increased lateral drag at the ice marginsthat can slow down ice flow and retreat. However, bed topography beneath the ice is not well-resolved and the jury is still out on whether current retreat is truly irreversible.

Antarctic ice shelf collapse is documented from the mid-1990s onward.

Vaughan, D. G., and C. S. M. Doake (1996), Recent atmospheric warming and retreat of ice shelves on the Antarctic Peninsula, Nature, 379, 328–331.

Scambos, T., C. Hulbe, and M. Fahnestock (2003), Climate‐induced ice shelf disintegration in the Antarctic Peninsula, in Antarctic Peninsula Climate Variability: Historical and Paleoenvironmental Perspectives, Antarct. Res. Ser., vol. 79, edited by E. Domack et al., pp. 79–92, AGU, Washington, D. C.

The current IPCC projections are not intentionally underestimated. We are still at a stage of discovering new processes that are important to the ice-ocean-climate system; therefore, taking a step forward of being able to incorporate important processes in models, to varying degrees, limits the uncertainty and magnitude of future changes. For example, recent numerical model work by Robel et al. (2019) has demonstrates the importance of a single ice-destabilizing process in sea-level projections that can increase the magnitude and uncertainty in sea-level scenarios. This is just one example of how a single process or condition impacts the (un)certainty in future sea levels and thus limits community planning that takes into account a large range of scenarios, in particular the high-end scenarios that will be more costly for mitigation infrastructure.

Although this was the conception, the idea that the Antarctic ice sheet was stable in the 1990s largely stems from a lack of continental scale observations provided by remote sensing and a lack of widespread in situ, on-ice observations. Therefore, late 20th century thought of a stable Antarctic ice sheet stemmed from negative evidence, rather than positive evidence supported by observations.

Using the geological record of Antarctic Ice Sheet behavior, the Ross Ice Shelf has collapsed in the past (Yokoyama et al., 2016, PNAS), likely in response to ocean and atmosphere warming. Therefore, we know that the Ross Ice Shelf, which currently protects large portion of the Antarctic Ice Sheet (Fürst et al., 2016, Nature Climate Change), is susceptible to collapse.

The vulnerable parts of the ice sheet are those that resting on beds that are below sea level; therefore, the ice itself is in contact with a warming ocean. The majority of the West Antarctic and ~30% of the East Antarctic sectors of the ice sheet are grounded below sea level.

This claim is flawed. Ice core records of past greenhouse gas and atmospheric temperature change (e.g. Monin et al., 2001, Science), coupled with records of ocean temperature and circulation changes (e.g. Skinner et al., 2010, Science), indicate that there are complex feedbacks between earth-atmosphere-ocean changes that lead to naturally variable greenhouse gas changes. In some cases during past deglaciations, increases in CO2 have lagged methane (CH4) increases and associated atmospheric temperature rise, owning to natural processes that induce greenhouse gas release into the atmosphere. This is not the case for twentieth century and beyond human-induced atmospheric CO2 and temperature increases.

Regardless of the source and cause of atmospheric CO2 increase, it will have a warming effect. Basic science does not change; CO2 is a greenhouse gas that is released into the atmosphere by burning of fossil fuels and leads to atmospheric warming.

This statement is false. The IPCC reports are written by a large number of international scientists to comprehensively summarize existing literature on climate change in the past, present, and future and its impacts on society. Although many countries are involved in the IPCC, the organization objectives and resulting publications are not biased by politics, but purely scientific.

Science is sound when similar numbers are reproduced multiple times by multiple people and, in some cases, using different methods. That is how a consensus is formed on any given topic.

This is correct. The Greenland Ice Sheet is losing mass primarily due to increased surface melting due to rising atmospheric temperatures, whereas the majority of the margin of west Antarctic Ice Sheet is directly in contact with a warming ocean and has experienced increases in melting around the margin of the ice sheet that leads to ice shelf thinning and ice sheet retreat.

References: Rignot, E., Box, J.E., Burgess, E. and Hanna, E., 2008. Mass balance of the Greenland ice sheet from 1958 to 2007. Geophysical Research Letters, 35(20).

Shepherd, Andrew, et al. "A reconciled estimate of ice-sheet mass balance." Science 338.6111 (2012): 1183-1189.

It is more accurate to use 'scientific community' rather than 'climate community' because scientific studies of climate change and responses to climate change are not just from the more narrow community of climate scientists, but from scientists across a variety of fields. Simply, the scientific community (biologists, atmospheric scientists, oceanographers, geologists, glaciologists, climatologists, etc.) have come to an overwhelming consensus that recent climate change is human-induced.

The causes of recent warming are not only based on global climate models. Observations from instrumental and proxy measurements also support that the accelerated rate of climate change (and associated ice mass loss and sea level change) is caused by human activity.

This is correct and supported by multi-disciplinary scientific studies that collectively capture the coupled response of the earth, atmosphere, ocean, and biological systems.

This is especially true for marine-terminating glaciers, meaning that the seaward-most margin of the glacier rests on a bed below sea level and, therefore, in direct contact with the ocean. Examples are glaciers in the Amundsen Sea, Antarctica such as Pine Island and Thwaites glaciers (Jacobs et al., 2011; Shepherd et al., 2004), currently experiencing rapid retreat that is associated with warm ocean water melting the glaciers and their floating ice shelves.

Jacobs, S.S., Jenkins, A., Giulivi, C.F. and Dutrieux, P., 2011. Stronger ocean circulation and increased melting under Pine Island Glacier ice shelf. Nature Geoscience, 4(8), pp.519-523.

Shepherd, A., Wingham, D. and Rignot, E., 2004. Warm ocean is eroding West Antarctic ice sheet. Geophysical Research Letters, 31(23).

This is supported by the relatively rapid (sub-decadal to decadal) changes in global ocean oxygen loss that are consistent with rapid changes in atmospheric greenhouse gas emissions and associated warming effects on the atmosphere and ocean, when compared to the longer-term context recorded in geological archives of past ocean variability.

Readers would benefit from more details on why portions of the reef are not as sensitive to bleaching. What causes spatial differences in bleaching? For example, Marshall and Baird (2000) demonstrate that bleaching sensitivity depends on the coral taxa.

This statement could benefit from scientific references for the contributions of anthropogenic versus natural (i.e. El Niño) ocean warming to observations of coral bleaching.

This statement highlights the major problem with this article. The authors do not support their claims with scientific references and data. Their logic is flawed and does not take into account basic scientific theories that explain, for example, the role of certain gases in causing a greenhouse effect and the negative impacts of high levels of greenhouse gases in the atmosphere. The authors' confusion of solid particulates in the atmosphere versus greenhouse gases results in many of misleading claims. So based on this statement and the lack of scientific references in this article, readers should be prompted to disregard the majority of claims presented here.

Climate change and poverty go hand in hand, as developing counties are disproportionately affected by climate change.

This is simply not accurate. Global warming is a global issue that, for example, affects global coastal populations, marine ecology, crop stability, and the area of habitable land. Humans, especially in countries with the largest carbon emissions, have been successfully altering the entire Earth system; therefore, climate change is currently the most global issue that we face and will continue to face in the coming centuries.

Authors should have stated what they mean by 'genuine pollutants.'

This is true. Habitable temperatures, however, do not mean comfortable temperatures and that all life can flourish. Habitable temperatures mean that it is physically and biologically possible for some kind of life can survive.

This is vastly incorrect.

Solid particulates and the gases listed do not influence climate change. The two major greenhouse gases are carbon dioxide and methane. Direct measurements from the atmosphere, such as from the Mauna Loa station, and measurements from 'fossil' air preserved as bubbles in ice cores indicate CO2 and CH4 have been increasing at unprecendented rates in post-industrial times. The concentrations of CO2 and CH4 in the atmosphere today are higher than they have been in the past 800,000 years, which is the age of the oldest ice core.

The idea that cutting carbon emissions is futile or too late appears to be common theme in some recent articles on climate change. This is simply not true considering carbon builds up in the atmosphere and has a lasting influence on global climate for decades to come. We can reduce future anthropogenic global warming in the coming decades and centuries by making an effort to cut emissions today, and that should be a catalyst for global policy change to cut emissions as soon as possible.

Although my background is not in economics, I would think relatively poor low-lying nations do not have the necessary resources to make their lands resilient to the effects of sea level rise. Yes, cutting carbon emissions and moving toward green energy is currently an expensive endeavor, but so is coastal management and engineering, especially for nations where the majority of people are below the poverty line and political corruption is already a problem. Therefore, the presented logic seems flawed, at least without presenting a 'cost-benefit' analysis between cutting global carbon emissions versus coastal engineering to mitigate the effects of sea level rise for low-lying coastal populations.

The article mentions sea level rise numerous times without providing a reference to the rates or trends of sea level rise for the Marshall Islands. Sea level in the Marshall Islands is rising at a rate of ~2.4-4.8 mm/yr, measured between 1968 to 2011. This is higher than 20th century global mean sea level rise of 1.5-1.9 mm/yr (IPCC AR5).

As wave energy and rising sea levels batter coastlines, the erosional products (i.e. sediments) can either be accreted onto the existing land or removed offshore into the deep ocean. Where the sediment is redistributed depends on a number of factors. Although sediment accretion can increase land area, it does little to change the elevation of low-lying islands, like the Marshall Islands. Therefore, people living in low-lying areas, even if there is historical land area gain, are still susceptible to inundation and damages due to storm waves, higher-than-usual tides (e.g. king tides), and sea level rise. These unconsolidated, loose sediments are also easily mobilized; therefore, localized land area gains by sediment accretion can be very dynamic on short timescales. This article could leave readers thinking that land area gains alone can mitigate the effects of sea level rise on low-lying coastal areas, but land elevation is what is really important.

There is a big misconception about the trigger of recent earthquakes in Oklahoma. Fracking in the United States has been used for several decades. However, the disposal of waste water into the subsurface has been directly linked to the recent Earthquakes in Oklahoma. A quick google scholar search on 'Oklahoma earthquakes' will bring up numerous articles that demonstrate this point. My family has lived in Oklahoma for decades and I can tell you first-hand that the increase in number of >3.0 magnitude earthquakes is unprecedented in the past 8 years.

The ability of greenhouse gases to trap heat in the atmosphere, the fact that loss of ice decreases how much energy is reflected from Earth's surface back to space, and ocean acidification due to uptake of CO2 into the ocean are all scientifically explained by chemical and physical processes. I am sure there are different definitions of 'the green movement', but any action that 'the green movement' can advocate for reduced greenhouse gas emissions has the potential to alter the physical, chemical, and biological processes that cause warming.

Desirability of a location has nothing to do with how safe it is from the effects of climate change.

Yes, there are dynamic changes and feedbacks within the climate system, which is why climate scientists study non-linear behavior so that we can better understand how the individual pieces work and how they fit together. This is precisely why we have a range of climate predictions for the future, which are constrained by climate change in the past through geological, instrumental, and historical observations and provide scientific-based predictions of climate change.

Climate science is based on physical, biological, and chemical processes. There are feedbacks between these processes such as biological consumption of atmospheric CO2 by photosynthesis. However, the idea of a self-regulated Earth system due to biological activity is not a common principle of climate science.

The 'it's too late to do anything about it' idea is socially (and environmentally) irresponsible. The carbon that humans have pumped into the atmosphere will have continued effects on global warming for the next decades to century due to the residence time of CO2 in the atmosphere. Therefore, without mitigation, we prolong anthropogenic warming of the atmosphere and ocean.

This statement is not founded by science.

Readers might not realize 'm' stands for 'million'.

Good point. Changes in ice load and Earth's rheology (thickness of the rigid outer layer and properties of the underlying mantle) are important for determining rates of rebound. Give the same ice load/deloading, rebound rates would be expected to be higher in areas of lower mantle viscosity or thinner crust than areas of higher mantle viscosity or thicker crust. Therefore, spatial (and temporal) variability in ice mass loss estimates from GPS stations must take into account Earth's rheology.

While it is important to recognize the potential sea level equivalents held up in current ice sheets, complete loss of the Greenland Ice Sheet by 2100 is not reasonable and would likely take thousands of years.

For a paleo-perspective, Greenland ice cores and ice sheet models demonstrate that parts (now which parts are up for debate) of the Greenland Ice Sheet did collapse during the last interglacial period (~125,000 years ago) when global mean atmospheric temperature was ~1 degrees C warmer than pre-industrial temperature; however, sectors of the ice sheet remained intact.

'draining and calving' is more appropriate

To expand on this statement, observations of ice mass loss indicate that the Greenland Ice Sheet contributes 0.33 [0.25-0.41] mm/yr to global sea level rise. Contributions from thermal expansion and glaciers outside of Antarctica and Greenland are are currently the major contributors to global sea level rise followed by contributions from the Greenland Ice Sheet.

'Ice sheet' is more accurate.

Although measuring how long CO2 stays in the atmosphere due to various sources and sinks, the IPCC AR3 gives an estimate of atmospheric CO2 residence time of 50-200 years. This means that CO2 already in the atmosphere will contribute to global warming, ice mass loss, and sea-level rise for the coming decades to centuries.

and global

This could be rephrased to be more quantitative by stating that the rate of local sea level rise in the area of 4.5 mm/yr (over the period between 1927 CE and 2015 CE) is larger than the rate global mean sea level rise of 3.3. mm/yr (over the period of 1994-2011).

I would like to see the support for this statement. Is this average storm wave height across the US coastline above a certain tidal datum?

Tides are not the only cause of variations in water levels. It would be better to use the all inclusive term 'water levels' here to encompass changes in coastal flooding due to longer-term sea level rise, tides, storms, etc.

Title is misleading. Wadhams suggests that the central Arctic will be ice free in the summer.

This is alarmist. Low-lying coastal communities will either have to modify or abandon the coast due to sea-level rise. It is true that developing countries will have less resources for coastal adaptation and will suffer more from rising sea level. However, it is ridiculous to assume that people living in developing countries will simply drown as they watch water levels rise. These communities will likely have to abandon the coast.

This range is not entirely accurate. Using different climate scenarios, global mean sea level is predicted to rise by 0.26 to 0.98 m by the end of the century. This does not include potential collapse of marine-based sectors of the Antarctic Ice Sheet, which could raise these estimates. Recent work suggests that Antarctica’s contribution to sea level could contribute >1 m to sea level rise on top of the IPCC AR5 estimates.

I would like to see the support for this statement.

This is a good point. Changes in one part of the Earth system due to warming are not in isolation and result in feedbacks in other parts of the Earth system.

Arctic sea ice is typically less than 4 m thick.

The use of ‘ice cap’ traditionally implies a body of ice on land that covers less area than an ice sheet; however, the article discusses sea ice, not an ice cap, which is floating ice that forms due to freezing of surface water.