It has indeed been hotter in years past

Temperature ...

Click on the Chart

     Discussion of natural climate cycles are appropriate, but we'll want to understand them along the timeline of modern humans and other life.  Significant changes in the past have brought mass extinctions and a restructuring of the ecosystem. Natural cycles are perhaps physically inevitable and in the queue for our consideration. Different natural cycles appear to occur on tens to tens of thousands of years periodicity and can fall in sync to exaggerate or mitigate the combined impact.

     It has indeed been hotter in years past, but humans weren't in existence yet, and the world was a radically different place.

     Separate from those natural cycles are the changes we see ourselves causing today.  The basic physics: if you add greenhouse gasses to an experimental sunlit atmosphere, it absorbs additional heat in proportion to the amount added.  At some threshold, its capacity to shed that heat is exceeded, and a runaway increase follows. 

     There are a number of unresolved questions regarding the timeline projection and the degree of impact, but there's little reason to suggest our children and grandchildren will not face difficulty in adapting.  That's one of our modern concerns regarding our ecosystem.

... and Life since there's more going on than just warming.

Tokyo-Yokohama, 37.8 million

Through most of history, everyone lived a rural lifestyle dependent on agriculture and hunting for survival. 

• In 1800, 3% of the world's population lived in villages of 5000 or more. 
• By 1900, about 14% were urbanites, and 12 cities had a million or more residents. 
• In 1950, 30% of the world's population lived in cities and, the number of cities with over 1 million people had grown to 83, each with its economically specialized segments and associated vulnerabilities.

Jakarta, Indonesia, 30.5 million

We've seen unusual urban growth. 

• It's 2017, and more than 50% of the world lives in cities. There are more than 400 cities over a million and 35 over 10 million. The more developed nations are about 75% urban (US-81%), while 45% of residents of less developed countries live in urban areas. 
• The trend is growing worldwide. We expect that 70% of the world population will be urban by 2050, and most urban growth will occur in less developed countries.

It's a bit naive to think there's no significant impact.  Did you know extinctions have accelerated along with population? 

At the turn of the 20th century some 100,000 tigers roamed throughout Asia. Today the last 3200 tigers in the wild are scattered across 7 percent of their former range, often in small “island” populations whose isolation puts them at risk of becoming inbred and imperils their long-term survival.  ~ Sharon Guynup

We're in a mass extinction spiral.  Harvard biologist E. O. Wilson estimates that 30,000 species per year (three species per hour) are being driven to extinction. The natural background rate is one extinction per million species per year (approximately 5-10 species per year).  Human-caused extinctions, most triggered by habitat destruction, are 100 - 1000 times the background rate according to one conservative statistical model.  (The actual numbers continue to be controversial)

The current mass extinction differs from all others in being driven by a single species rather than a planetary or galactic physical process. When the human race — Homo sapiens sapiens — migrated out of Africa, waves of extinction soon followed. The colonization-followed-by-extinction pattern can be seen as recently as 2,000 years ago, when humans colonized Madagascar and quickly drove elephant birds, hippos, and large lemurs extinct.

The first wave of extinctions targeted large vertebrates hunted by hunter-gatherers. The second, larger wave began 10,000 years ago when the advent of agriculture caused a population boom and a need to plow wildlife habitats, divert streams, and maintain large herds of domestic cattle. The third and largest wave began in 1800 with the harnessing of fossil fuels. With enormous, cheap energy at its disposal, the human population grew rapidly past 1 billion in 1800 to 2 billion in 1930, 4 billion in 1975, and over 7 billion today. We'll reach 8 billion by 2020 and 9 to 15 billion (likely the former) by 2050.

"No population of a large vertebrate animal in the history of the planet has grown that much, that fast, or with such devastating consequences to its fellow earthlings. Humans’ impact has been so profound that scientists have proposed that the Holocene era be declared over and the current epoch (beginning in about 1900) be called the Anthropocene: the age when the "global environmental effects of increased human population and economic development" dominate planetary physical, chemical, and biological condition."

• Humans annually absorb 42% of the Earth’s terrestrial net primary productivity, 30% of its marine net primary productivity, and 50% of its fresh water.*
• Forty percent of the planet’s land is now devoted to our food production, that's up from 7% in 1700.*
• Fifty percent of the planet’s land mass has been transformed for human use.*
• More atmospheric nitrogen is now fixed by humans than all other natural processes combined.*  Although carbon dioxide may get more press, “the nitrogen cycle has been altered more than any other basic element cycle.”

*Vitousek, P. M., H. A. Mooney, J. Lubchenco, and J. M. Melillo. 1997. Human Domination of Earth's Ecosystems. Science 277 (5325): 494–499; Pimm, S. L. 2001. The World According to Pimm: a Scientist Audits the Earth. McGraw-Hill, NY; The Guardian. 2005. Earth is All Out of New Farmland. December 7, 2005.

• Coral reefs are declining rapidly: destructive fishing practices and runoff from overdevelopment all take a toll, weakening the reefs and making them more susceptible to storms and diseases. The latest reports state that as much as 27 percent of monitored reef formations have recently been lost and as much as 32 percent are at risk of being lost before 2050.

• Coral reefs cover only about 0.1 percent of the ocean bottom but are vital to ocean life: 9 million marine species, including 4,000 kinds of fish, rely on coral reefs for food or shelter. Further, reefs form a central pillar of many countries' economies, supporting fishing industries and protecting coastlines from storm surges.

• Pelagics (tuna and the like) are now at risk due to overfishing and pollution of breeding areas.  Total adult biomass summed across all monitored pelagic populations has declined globally by 52.2% from 1954 to 2006.  Certain regions have seen 90% decline in population causing malnutrition and starvation among indigenous fishing communities.*

*Global population trajectories of tunas and their relatives Maria José Juan-Jordá, Iago Mosqueirad, Andrew B. Cooperf, Juan Freirea, and Nicholas K. Dulvyc, Grupo de Recursos Marinos y Pesquerías, Facultad de Ciencias, Universidad de A Coruña, 15009 A Coruña, Spain; Earth to Ocean Research Group, Department of Biological Sciences, Simon Fraser University, Burnaby, BC, Canada; Centre for Environment, Fisheries & Aquaculture Science, Lowestoft Laboratory, Lowestoft, United Kingdom; European Commission, Joint Research Center, Institute for the Protection and Security of the Citizen/Maritime Affairs Unit; School of Resource and Environmental Management, Simon Fraser University, Burnaby, BC, Canada

Suggesting that the changes we've brought are minor or inconsequential goes perhaps beyond naive to some measure of indifference or the inattentive privilege of wealth.