This case is not quite as bad as the 'Worst Case Scenario', but may be more agonizing for humanity, because it plays on fear and emotion resulting in a more long drawn out case of failure than does the more direct failure.  So 'worst' is defined here in terms of degree of immediate impact to Earth's biosphere and not 'how agonizing it is for humans'.

During the later part of the first decade of the new millennium people looked no further than their own immediate sphere of influence to determine their happiness.  They looked at their bank balance, attended their kids birthday parties and on occasion invited family or friends over for dinner.  On their sabbath many attended religious ceremonies at their places of worship.

People believed the hype and bad science promulgated by the entrenched pundits of energy production.   They bought into these paradigms of "nothing is wrong" and "we have everything under control".  The pundits depended on 'out of sight / out of mind' and employed tactics similar to those used by the tobacco industry.  Just like lemmings, people caught up in their own little issues - ignored where they collectively were headed.  Humanity's common heritage, 65 million years in the making, was destroyed.

In 2007 the President of the United States announced during that countries 'State of the Union' address as called for in its constitution: that "America is on the verge of technological breakthroughs that will enable us to live our lives less dependent on oil. And these technologies will help us be better stewards of the environment, and they will help us to confront the serious challenge of global climate change.".   He did not mention what those technologies were.   Later in the address he asked that congress help reduce the consumption of gasoline by 20% because that amount is equal to the amount of oil imported from the Middle-East.   People found out later that those new technologies came in the form of algae farms to consume the carbon dioxide produced by energy producers.  Those farms required thousands of acres of real estate to handle the output of a single power plant.  Others tried other sequestration techniques that held yet different consequences.

The only political actions were framed in the context of "dependence on foreign oil" - not in terms of correcting "Climate Change".  Constituents thought that was the only issue.  They thought that because they did not understand the problems with the Oceans nor did they perceive the potential threats from other corners of the biosphere.  Their peers joined in the chorus of ignorance.

People were mislead to believe that the band-aids were permanent solutions.  Never did they demand a strategy to shift energy production to 100% non-polluting sources.  Carbon Dioxide was never classified as a pollutant.  The energy companies continued to claim to be 'clean' because CO2 was never officially recognized as a pollutant.  The traditional 'free pass' continued and people were confused about the problem with the evidence nicely hidden from view in the corners of social discussion.   No one worked on the solution because they didn't think one was needed.  Why?  Because they didn't believe there was a problem. 

Energy producers convinced everyone that the right thing to do was to put carbon dioxide scrubbers on every power facility they had.  These scrubbers collected all the carbon dioxide from the emissions.  The power companies then sold that CO2 to other companies who used it to manufacture calcium carbonate.  The calcium carbonate was in turn used to create everything from bricks to building materials to reef restoration projects.  This new infrastructure added to the costs associated with producing energy.  Energy remained tied to natural resources in the Earth.   Energy costs soared.

Not only were existing energy customers struggling with Energy costs it was now assured that energy would never be deployed to the more remote areas.  Some areas of the grid were shut down because those customers could not afford the cost of power, despite superficial programs from energy producers, generously targeting "low income customers".

Energy producers argued successfully that humanity did not need to go to space to produce power.  That terrestrial sources could be made to be clean and that economies could afford the new infrastructure to assure clean emissions.

The point the general public missed was the small fact that carbon dioxide already in the atmosphere was killing them and the "new infrastructure" only focused on 'future CO2 emissions'.  It did nothing about the CO2 introduced into the biosphere since the industrial revolution began.  Permafrost continued to thaw.  Gas hydrates slowly released their reservoirs and polar ice, as well as glaciers, continued their retreat.

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By the time the general public recognized the issues with energy production and that many criteria requirements had to be implemented during the design of that sector of the economy it was too late.  The economy simply could not afford the complexities of this infrastructure on a global scale.  The vagaries between consumer location and physical impact to more remote areas of the biosphere never got connected in the mind of global society.  Social strife increased between the 'haves' and 'have nots' in society.  Wars broke out.  The economy supporting the energy production facilities collapsed.   Energy producers were forced to focus on financial ROI and not the biosphere.  Shareholders from the "have camp" demanded their investment value and returns. 

In the time between the beginning of the 21st century and early in the 22nd, carbon dioxide continued to build in the atmosphere.  Commercial fish populations died about mid-21st century and people looked elsewhere for protein sustenance previously provided by those fishes.  The level of the oceans began to rise.   Those living near coastal areas were displaced and moved inland.  Further stressing the food problem.  Real estate needed for the increasingly important agricultural products became critical.   Power generation facilities consumed thousands of acres with algae farms in an attempt to process the CO2 that they belched from their facilities.  Carbon dioxide scrubbing facilities that would have been used to clean the air were used instead on 'emission reduction' projects.  What was in the atmosphere stayed in the atmosphere to exacerbate the problem.   Instead of eating tuna people ate green algae derivatives.  They were taught that eating algae was good for the environment and good for you too. 

As the oceans warmed they too became just a little more corrosive to metal in them.  Shipwrecks from long forgotten wars began breaking down faster in the warmer seas.  The contaminants they sequestered were released into the environment and became part of the food chain.  Especially in the North Eastern Atlantic.  Algae blooms became more frequent.  Dead Zones more predominant.  The oceans became less tolerant of life.  Except the cyano bacteria based life forms from a millennium ago.  Those thrived and killed species familiar to humanity.

Lack of food, displaced real estate, pressures on farming and living space conspired to create unprecedented levels of misery for peoples everywhere.

Ocean acidity continued to increase.  All the struggles, strife and tribulations escalated.  Add an order of magnitude to the situations and continue reading the 'Worst Case Scenario' as the events would unfold down a similar pattern once the economy could no longer support the infrastructure necessary to both pollute itself and then try to clean it up.  Some how people just didn't understand that the only strategy was to not pollute in the first place.