“Anyone who believes exponential growth can go on forever in a finite world is either a madman or an economist” is a quote that has been credited in 1973 to English-born American economist Kenneth E. Boulding (1910-1993). It’s not known when Boulding first said the quote.
 
The Guardian (London, UK) on January 21, 2019, reported English broadcaster and natural historian David Attenborough repeating the quotation at the World Economic Forum meeting in Davos, Switzerland:
 
“Speaking to journalists after his speech, Attenborough warned that economic models needed to change. ‘Growth is going to come to an end, either suddenly or in a controlled way,’ he explained, citing the old joke that anyone who thinks you can have infinite growth in finite circumstances is ‘either a madman or an economist’.”
   
     
Wikipedia: Kenneth E. Boulding
Kenneth Ewart Boulding (/ˈboʊldɪŋ/; January 18, 1910 – March 18, 1993) was an English-born American economist, educator, peace activist, and interdisciplinary philosopher. He published over thirty-six books and over one hundred and twelve articles. Boulding was the author of two Citation Classics: The Image: Knowledge in Life and Society (1956) and Conflict and Defense: A General Theory (1962). He was cofounder of general systems theory and founder of numerous ongoing intellectual projects in economics and social science.
 
Wikiquote: Kenneth Boulding
Anyone who believes exponential growth can go on forever in a finite world is either a madman or an economist.
. Attributed to Kenneth Boulding in: United States. Congress. House (1973) Energy reorganization act of 1973: Hearings, Ninety-third Congress, first session, on H.R. 11510. p. 248
     
8 October 1973, El Paso (TX) Times, “Grumbling About Growth” (editorial), pg. 4-A, col. 1:
Is such explosive growth possible? Moreover, is it desirable? Economist Kenneth E. Boulding once said that anyone who believes exponential growth can go on forever in a finite world is either a madman or an economist. Conomists have always been the gurus of growth but many have begun to doubt the faith.
 
Google Books
Energy Reorganization Act of 1973: Hearings, Ninety-third Congress, First Session, on H.R. 11510
By United States. Congress. House. Committee on Government Operations. Legislation and Military Operations Subcommittee
Washington, DC: U.S. Government Printing Office
1973
Pg. 239:
That is why I quoted Kenneth Boulding, who always seems to have a fine turn of phrase, that anyone who believes growth can go on forever is either a madman or an economist.
Pg. 248:
As the economist, Kenneth Boulding has remarked, “anyone who believes exponential growth can go on forever in a finite world is either a madman or an economist.”
   
Google Books
Awakening from the American Dream:
The social and political limits to growth
By Rufus E. Miles
New York, NY: Universe Books
1976
Pg. 11:
Anyone who believes that exponential growth can go on forever is either a madman or an economist, according to the distinguished economist Kenneth Boulding.
 
Fall 1980, National Forum (Baton Rouge, LA), “The Energy Crisis and Economic Models” by Neil E. Harl, pg. 42, col. 1:
As Kenneth Boulding, himself an economist of some note, said, “anyone who believes exponential growth can go on forever in a finite world is either a madman or an economist.”
 
Google Groups: sci.econ
The Necessity of Capitalist Growth
Alastair McKinstry
11/14/96
(...)
Anyone who believes exponential growth can go on forever in a finite world is either a madman or an economist - Kenneth Boulding, economist.

Google Groups: can.politics
Pay Taxes? Why?
Daniel Lavigne
12/8/01
(...)
Anyone who believes exponential growth can go on forever in a finite world is either a madman or an economist.揖enneth Boulding
 
The Guardian (London, UK)
David Attenborough tells Davos: ‘The Garden of Eden is no more’
Human activity has created a new era yet climate change can be stopped, says naturalist
Graeme Wearden in Davos
Mon 21 Jan 2019 14.19 EST
(...)
Speaking to journalists after his speech, Attenborough warned that economic models needed to change. “Growth is going to come to an end, either suddenly or in a controlled way,” he explained, citing the old joke that anyone who thinks you can have infinite growth in finite circumstances is “either a madman or an economist”.