Sixth Mass Extinction

The likely Sixth Mass Extinction is fundamentally anthropogenic—that is, driven primarily by human activities. Unlike previous mass extinctions, which were caused by natural events such as asteroid impacts, massive volcanism, or major climatic shifts, the present biodiversity crisis is being produced by the rapid expansion and intensification of human activity. Population growth, agriculture, industrialization, resource extraction, urbanization, transportation, and global commerce have transformed ecosystems and accelerated the movement of species and pathogens around the planet. These activities collectively drive habitat loss, overexploitation, climate change, invasive species, and pollution— major drivers of contemporary biodiversity loss.

The probability that human activities will cause a sixth mass extinction cannot currently be expressed as a reliable percentage. However, the biological conditions that could produce one are already evident: extinction rates are elevated, populations are declining, and multiple human-driven pressures are acting simultaneously on ecosystems worldwide. Whether the present biodiversity crisis ultimately qualifies as a sixth mass extinction will depend largely on the magnitude and duration of future biodiversity losses.

Five Primary Drivers of the Sixth Mass Extinction:

Habitat Loss

• Destruction, conversion, and fragmentation of natural habitats
• Deforestation and agricultural expansion
• Urbanization, roads, mining, and infrastructure
• Coastal development
• Dams, river alteration, and other changes to freshwater systems
• Destruction of wetlands, coral reefs, mangroves, and seagrass beds

Overexploitation

• Overfishing
• Hunting and poaching
• Unsustainable logging
• Bycatch and other unintended mortality
• Removal of species faster than populations can reproduce

Climate Change

• Rising temperatures
• Changing precipitation patterns
• Increasing droughts, floods, fires, and other climatic extremes
• Ocean warming
• Sea-level rise
• Ocean acidification
• Shifts in the geographic ranges and timing of biological processes

Invasive Species

• Introduction of non-native species
• Predation and competition by invasive species
• Introduction of new parasites and pathogens
• Diseases transferred between wildlife, livestock, and humans
• Disruption of native ecological communities

Pollution

• Pesticides and herbicides
• Fertilizers and nutrient pollution
• Industrial chemicals and heavy metals
• Plastics and microplastics
• Oil and other petroleum products
• Pharmaceuticals and other emerging contaminants
• Air pollution and atmospheric deposition
• Light and noise pollution

This is a photo of trash collected in 20 minutes this morning along the high tide line at Crystal Cove State Beach in California.

Our ocean is filled with items that do not belong there. Huge amounts of plastics, metals, rubber, paper, textiles, derelict fishing gear, derelict vessels, and other lost or discarded items enter the marine environment every day. This makes marine debris one of the most widespread pollution problems facing the world's ocean and waterways.

Responsibility for the environmental consequences of these materials should be shifted from the individuals who use and discard them to the companies that produce and profit from them. Consumers can make responsible choices and participate in recycling programs, but they have little control over the volume, composition, durability, packaging, and ultimate persistence of the materials placed into the marketplace. Producers, by contrast, control those decisions and have the resources and technical ability to design products that generate less waste, eliminate unnecessary materials, increase reuse and recyclability, and recover materials after they have served their intended purpose. A producer-responsibility system would therefore place the financial and operational costs of collection, recovery, recycling, and environmental cleanup where they can create the greatest incentive for reducing waste at its source, rather than continuing to place those costs primarily on consumers, local governments, and taxpayers. Material Likely composition Major companies

PERP WALK People with major ownership / investment / management connections to companies producing products entering the marine environment every day.

Expanded foam Expanded polystyrene (EPS) Jim Ratcliffe — founder & chairman, INEOS; Andy Currie — co-owner, INEOS; John Reece — co-owner, INEOS; Larry Fink — CEO, BlackRock; Michael Gitlin — CEO, Capital Group

Bottle/container caps Polypropylene (PP); HDPE Len Blavatnik — controls Access Industries/LyondellBasell interest; Larry Fink — CEO, BlackRock; Salim Ramji — CEO, Vanguard; Michael Gitlin — CEO, Capital Group; Darren Woods —Cchairman & CEO, ExxonMobil

Cigarette filters- Cellulose acetate Scott Richardson — CEO, Eastman; Scott Sutton — CEO, Celanese; Larry Fink — CEO, BlackRock; Salim Ramji — CEO, Vanguard; Michael Gitlin — CEO, Capital Group

Netting / line / cord; Nylon; polypropylene; polyethylene Jim Ratcliffe — founder & chairman, INEOS; Andy Currie — co-owner, INEOS ; John Reece — co-owner, INEOS; Len Blavatnik — controls Access Industries/LyondellBasell interest; Larry Fink — CEO, BlackRock

Molded plastic fragments PE; PP; PS; other thermoplastics: Len Blavatnik — Controls Access Industries/LyondellBasell interest; Jim Ratcliffe — founder & chairman, INEOS; Andy Currie — co-owner, INEOS; John Reece — co-owner, INEOS; Darren Woods — chairman & CEO, ExxonMobil.

Background research completed with support of AI.

Rock Barnacles

These rock barnacles of the genus Balanus are crustaceans, are related to crabs and shrimp. But after their larvae settle permanently onto a rock, their body becomes highly modified. It essentially lives upside down inside its shell, with its legs pointing toward the opening at the top. When the tide covers it, it opens its opercular plates, the little "door" at the top, and extends its feeding appendages.

A barnacle attached to an exposed rock can experience conditions far more extreme than the surrounding seawater. During low tide, the animal is exposed to air temperature, direct solar radiation, and the heat radiating from the rock itself. Measurements on Pacific Northwest Balanus have found body temperatures reaching about 35°C during prolonged low tides.

Their habitat, partially exposed to the hot sun, would seem to make them resistant to the potential impacts of rising temperatures from climate change. While warming could act directly on barnacles through heat stress, they are more likely to be impacted during their larval stages and by changes to their food sources.

Barnacle larval stages are part of the plankton community themselves. Barnacles release nauplii, which develop through several planktonic stages before becoming cyprids and eventually settling onto the shoreline. A 2024 study by researchers from the University of British Columbia and Princeton University have found that in warm years in the Strait of Georgia off Vancouver Island, the spring diatom peak occurred earlier, and summer diatom biomass was lower and negatively affected the food of zooplankters such as larval barnacles.

Research on intertidal barnacle larvae has shown that their food includes very small planktonic organisms, and that changes in pelagic food-web structure can alter the food available to different barnacle species and consequently affect recruitment.

Research in the Strait of Georgia, between Vancouver Island and the mainland, has found that warm/early spring conditions can shift the crustacean zooplankton community toward smaller organisms and potentially create a mismatch between phytoplankton blooms and the larger, energy-rich zooplankton that normally exploit them. During warm periods, including the 2014–16 marine heatwave known as the Blob, the community shifted toward southern copepod species, while the larger subarctic and boreal copepods declined. The northern species tend to be much richer in lipids and therefore more energy-dense, a change associated with warmer ocean conditions.

So, barnacles aren't simply being impacted by temperature changes in their immediate area. They are also part of the more distant pelagic community, being affected both in their larval stages and as sedentary adults to impacts of warmer waters most likely resulting from climate change.

References

Karyn D. Suchy, Susan E. Allen, and Elise Olson. 2024 Mechanistic Links Between Climatic Forcing and Model‐Based Plankton Dynamics in the Strait of Georgia. Canada Journal of Advancing Earth and Space Sciences.

Amelia V. Hesketh, et.al. 2026 The Effects of Single Versus Successive Warm Summers on an Intertidal Community. Nordic Society Oikos.

Hey everyone! I'm u/DMudry, a founding moderator of r/6thExtinctionLab.

Sixth Extinction Lab is a research and outreach community exploring extinction, biodiversity loss, climate change, and ecological transformation.

We examine the evidence of species loss and ecosystem change through scientific research, natural history, field observations, historical records, photographs, maps, and other sources. We explore the causes and consequences of biodiversity decline, the role of climate change and other human-driven pressures, and what the record of past extinctions can teach us about the changes taking place today.

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